[PATCH v16 0/5] Add RMPOPT support.

[PATCH v16 0/5] Add RMPOPT support.

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

In the SEV-SNP architecture, hypervisor and non-SNP guests are subject
to RMP checks on writes to provide integrity of SEV-SNP guest memory.

The RMPOPT architecture enables optimizations whereby the RMP checks
can be skipped if 1GB regions of memory are known to not contain any
SNP guest memory.

RMPOPT is a new instruction designed to minimize the performance
overhead of RMP checks for the hypervisor and non-SNP guests.

RMPOPT instruction currently supports two functions. In case of the
verify and report status function the CPU will read the RMP contents,
verify the entire 1GB region starting at the provided SPA is HV-owned.
For the entire 1GB region it checks that all RMP entries in this region
are HV-owned (i.e, not in assigned state) and then accordingly updates
the RMPOPT table to indicate if optimization has been enabled and
provide indication to software if the optimization was successful.

In case of report status function, the CPU returns the optimization
status for the 1GB region.

The RMPOPT table is managed by a combination of software and hardware.
Software uses the RMPOPT instruction to set bits in the table,
indicating that regions of memory are entirely HV-owned.  Hardware
automatically clears bits in the RMPOPT table when RMP contents are
changed during RMPUPDATE instruction.

For more information on the RMPOPT instruction, see the AMD64 RMPOPT
technical documentation.

As SNP is enabled by default the hypervisor and non-SNP guests are
subject to RMP write checks to provide integrity of SNP guest memory.

This patch-series adds support to enable RMP optimizations for up to
2TB of system RAM across the system and allow RMPUPDATE to disable
those optimizations as SNP guests are launched.

Support for RAM larger than 2 TB will be added in follow-on series.

This series also adds support to disable CPU hotplug while SNP is
active, as the SEV firmware enumerates CPUs at SNP initialization and is
not aware of the OS bringing CPUs online or offline afterwards.  This
also keeps the set of CPUs stable for the asynchronous RMPOPT scan, so
the per-core RMPOPT_BASE MSRs programmed during setup remain valid.

This series also introduces support to re-enable RMP optimizations
during SNP guest termination, after guest pages have been converted
back to shared.

RMP optimizations are performed asynchronously by queuing work on a
dedicated workqueue after a 10 second delay.

Delaying work allows batching of multiple SNP guest terminations.

Once 1GB hugetlb guest_memfd support is merged, support for
re-enabling RMPOPT optimizations during 1GB page cleanup will be added
in follow-on series.

v16:
- 3/5 (Initialize RMPOPT MSRs): clear X86_FEATURE_RMPOPT when segmented RMP
  is enabled but its probe fails, so the initcall does not set up RMPOPT for
  a system that will not bring up SNP.  Program the RMPOPT_BASE MSRs only when
  RMPOPT_EN is not already set on the local CPU, so guest teardown skips
  reprogramming rather than reprogramming the MSRs on every teardown.

  Review feedback from Sashiko AI.

v15:
- 3/5 (Initialize RMPOPT MSRs): rename snp_setup_rmpopt() to
  snp_enable_rmpopt(); program each core's RMPOPT_BASE only when it is not
  already set.
- 4/5 (async RMPOPT): split setup from enable -- an initcall allocates the
  workqueue and computes the (fixed) optimization range once, and
  snp_enable_rmpopt() programs the RMPOPT_BASE MSRs and queues the
  optimization pass.  Gate rmpopt_capable() on a static rmpopt_enabled bool
  instead of an if (rmpopt_wq) check and drop rmpopt_wq_mutex.  Queue both
  the initial and the teardown pass with mod_delayed_work().
- 5/5 (Re-enable on guest shutdown): call snp_enable_rmpopt() on guest
  teardown instead of a separate snp_rmpopt_all_physmem().

  This is a full resend rather than a 4/5-5/5 reply because patch 3 changed
  as part of the setup/enable split.

  Review feedback from Borislav Petkov.

v14:
- 3/5 (Initialize RMPOPT MSRs): remove rmpopt_disable() and the RMPOPT_BASE
  teardown from this patch.  RMPOPT is now set up once and not torn down, so the
  RMPOPT_BASE MSRs are left in place on shutdown; the (now minimal) disable path
  moves to 4/5.
- 4/5 (async RMPOPT): rework the setup/teardown -- initialize once and do not
  tear it down.  rmpopt_disable() now only cancels the pending re-optimization
  pass.  Use a dedicated per-CPU workqueue (WQ_PERCPU) and drop the
  migrate_disable()/migrate_enable() around the local warm-up scan.  Add a
  binutils-version comment above the RMPOPT .byte encoding and trim redundant
  comments and the 2 TB pr_info().  Reword the subject to "Perform RMP
  optimizations asynchronously".
- 5/5 (Re-enable on guest shutdown): move the call-site comment onto the
  snp_rmpopt_all_physmem() definition and simplify the RMPOPT_WORK_TIMEOUT
  comment.
- Correct the Suggested-by/Reviewed-by tags across the series.

  Review feedback from Borislav Petkov.

v13:
- 3/5 (Initialize RMPOPT MSRs): use cpu_primary_thread_mask directly instead of
  building a local rmpopt_cpumask -- all primary threads are online while SNP is
  active, so the two are equivalent.  Rename snp_cleanup_rmpopt() to
  rmpopt_disable().
- 4/5 (async RMPOPT): drop the leader/follower bookkeeping.  Warm the RMP scan
  cache once, then fan the RMPOPT out to cpu_primary_thread_mask; re-running
  RMPOPT on the warm-up CPU is a cache hit, so the separate follower cpumask and
  the cpumask_andnot() are no longer needed.  Rename rmpopt_work_handler() to
  do_rmpopt_work() and drop the now-unused this_cpu.
- Add Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com> to the series.

  Review feedback from Borislav Petkov.

v12:
- Merged the former "Add interface to re-enable RMP optimizations" and
  "KVM: SEV: Perform RMP optimizations on SNP guest shutdown" patches into a
  single patch (now 5/5), since the interface has no user without the KVM
  caller.  The series is now 5 patches.
- 2/5 (Disable CPU hotplug): drop a stray reference to later patches from the
  commit message and trim the snp_prepare() comment.  Move cpu_hotplug_enable()
  to the end of snp_shutdown(), after clear_rmp() and the mfd_reconfigure() IPI,
  so no all-CPU operation runs after hotplug is re-enabled.
- 3/5 (Initialize RMPOPT MSRs): restructure snp_probe_rmptable_info() so the
  contiguous probe (which clears X86_FEATURE_RMPOPT) is the common fall-through,
  also covering X86_FEATURE_SEGMENTED_RMP advertised but disabled by firmware.
  Move snp_setup_rmpopt() to the end of __sev_snp_init_locked().  Give
  snp_cleanup_rmpopt() its own short comment in snp_shutdown().
- 4/5 (async RMPOPT): document the optimization trigger points in the commit
  message.  Rename enum rmpopt_function to rmpopt_op_type.  Merge __rmpopt() into
  rmpopt() and replace rmpopt_smp() with a new rmpopt_scan_range() that loops as
  the on_each_cpu() callback, so the follower scan issues one IPI per core rather
  than one per 1GB.  Use u64 for physical addresses.  Allocate the follower
  cpumask once at setup.  Document rmpopt_wq as the setup sentinel.  Move the
  RMPOPT_WORK_TIMEOUT define to the guest-shutdown patch (its only user) as
  (10 * MSEC_PER_SEC).  Remove a spammy pr_info() and reword comments.
- 5/5 (Re-enable RMP optimizations on SNP guest shutdown): document why
  re-optimization is driven by guest teardown (the only event that returns
  guest memory to hypervisor ownership); reword the commit message
  (s/clear/disable/ for optimizations, drop "Conversely").

  Review feedback from Borislav Petkov.

v11:
- Reordered so "Disable CPU hotplug while SNP is active" (2/6) precedes
  "Initialize RMPOPT configuration MSRs" (3/6): the RMPOPT setup/cleanup code is
  then introduced with CPU hotplug already disabled and never takes
  cpus_read_lock().
- 1/6 (cpufeatures): drop the tools/arch/x86/include/asm/cpufeatures.h change and
  adopt the commit message as applied by Boris.
- 2/6 (Disable CPU hotplug): reword the commit message.  Drop the redundant
  cpus_read_lock()/cpus_read_unlock() in snp_prepare() in this same patch -- with
  hotplug disabled the online CPU mask is stable, so the read lock is not needed
  and hotplug handling has no hole when bisecting.
- 3/6 (Initialize RMPOPT MSRs): replace the rmpopt_capable bool with a small
  helper local to arch/x86/virt/svm/sev.c --
  cpu_feature_enabled(X86_FEATURE_RMPOPT) && cc_platform_has(CC_ATTR_HOST_SEV_SNP)
  -- clearing X86_FEATURE_RMPOPT for a contiguous (non-segmented) RMP in
  snp_probe_rmptable_info() (runs at BSP init, before alternatives).  Rename
  rmpopt_cleanup() to snp_cleanup_rmpopt() to match snp_setup_rmpopt().  Both are
  introduced without cpus_read_lock() (hotplug is already disabled by 2/6).
  Simplify the RMPOPT_BASE comments.  Drop the now-unused <asm/sev.h> include from
  core.c.
- 4/6 (async RMPOPT): the follower scan is likewise introduced without
  cpus_read_lock().  Drop the cond_resched() calls (nops on x86).  On
  re-initialization after a legacy SNP shutdown, re-queue the optimization pass
  instead of skipping it.  pr_warn() on cpumask allocation failure.

  Review feedback from Borislav Petkov and K Prateek Nayak.

v10:
- Rework the CPU-hotplug patch (3/6): disable CPU hotplug in
  snp_prepare(), before SnpEn is set, instead of late in
  __sev_snp_init_locked(), so no CPU can come online without SnpEn during
  SNP initialization (per upstream review).  Tie hotplug to SnpEn: it
  stays disabled while SnpEn is set -- including across a failed SNP_INIT
  and across the legacy SNP_SHUTDOWN_EX path -- and is re-enabled only
  once the firmware clears SnpEn on the x86_snp_shutdown path.  Drop the
  separate idempotent flag: snp_prepare() re-enables hotplug on its own
  early failure, and a kexec target that boots with SnpEn already set
  disables hotplug once in snp_rmptable_init().  Reword the commit log and
  comments accordingly.
- Emit a pr_warn() in rmpopt_work_handler() (4/6) when the follower
  cpumask allocation fails, instead of silently skipping the optimization
  pass.

  Sashiko AI upstream review identified several of the above issues.

v9:
- Rename rmpopt_configured to rmpopt_capable.
- Make rmpopt_cpumask a cpumask_var_t (allocated/freed at setup/cleanup)
  instead of a static cpumask_t.
- Drop the v8 WARN_ON_ONCE() on the RMPOPT_BASE writes; use a plain
  wrmsrq_on_cpu(), matching the SNP MSR-write convention in this file.
- Disable CPU hotplug with cpu_hotplug_disable()/cpu_hotplug_enable()
  (per tglx); re-enable only on the full x86_snp_shutdown path.
- Simplify rmpopt_work_handler() to a single leader-then-followers path:
  with CPU hotplug disabled while SNP is active and snp_prepare()
  requiring all CPUs online when RMPOPT_BASE is programmed, every core is
  always programmed, so the explicit-leader fallback is now unreachable.
  Drop it along with the v8 work_on_cpu()/rmpopt_leader_fn() helper.
- Drop the debugfs interface (was patch 7/7) and its report-only
  plumbing; observability will be revisited after this series is merged.
- Restrict snp_rmpopt_all_physmem()'s export to the kvm-amd module.
- Use scoped_guard(cpus_read_lock) for the per-CPU MSR and follower
  loops.

  Sashiko AI upstream review identified several of the above issues.

v8:
- Add a new patch to disable CPU hotplug while SNP is active, keeping
  the CPU set stable for the RMPOPT work handler.
- Drop the setup_clear_cpu_cap(X86_FEATURE_RMPOPT) calls; the
  rmpopt_configured bool is the runtime guard.
- WARN_ON_ONCE() on the RMPOPT_BASE MSR writes that previously ignored
  their return value.
- Simplify rmpopt_work_handler() by removing the explicit-leader
  fallback: with CPU hotplug disabled while SNP is active and
  snp_prepare() requiring all CPUs online when RMPOPT_BASE is programmed,
  every core is always programmed, so the running CPU can always be the
  leader.  This drops the smp_call_function_single() fallback (and with
  it the AB-BA deadlock and IRQ-latency concerns) and collapses the
  leader selection into a single leader-then-followers path.
- Use mod_delayed_work() in snp_rmpopt_all_physmem() so the batching
  delay tracks the last SNP guest termination.

  Sashiko AI code review identified several of the above issues.

v7:
- Sync tools/arch/x86/include/asm/cpufeatures.h to mirror the kernel
  header for X86_FEATURE_RMPOPT.
- Fix commit title to use X86_FEATURE_RMPOPT to match the code
  (was X86_FEATURE_AMD_RMPOPT).
- Add static bool rmpopt_configured, set only when segmented RMP setup
  succeeds in setup_rmptable().  Check rmpopt_configured alongside
  cpu_feature_enabled(X86_FEATURE_RMPOPT) in snp_setup_rmpopt() and
  snp_rmpopt_all_physmem(), because setup_clear_cpu_cap() is unreliable
  after alternatives are patched.  Add snp_clear_rmpopt_configured()
  called from amd_cc_platform_clear() when CC_ATTR_HOST_SEV_SNP is
  cleared.  Do not use __ro_after_init on rmpopt_configured since the
  writer snp_clear_rmpopt_configured() is not __init.
- Add cond_resched() to all three leader loops in rmpopt_work_handler()
  to prevent soft lockups on systems with up to 2TB of RAM.
- Add comment above __rmpopt() documenting the RMPOPT instruction
  encoding (F2 0F 01 FC) and register interface (RAX = system physical
  address input, RCX = operation type input, RFLAGS.CF = output).
  Note: RMPOPT does not modify RAX unlike PVALIDATE/RMPUPDATE, so
  the existing "a" (input-only) constraint is correct.

  Sashiko AI code review identified several of the above issues.

v6:
- Drop wrmsrq_on_cpus() helper; use for_each_cpu() with wrmsrq_on_cpu()
  instead, as RMPOPT_BASE MSR programming is not performance-critical.
- Rewrite rmpopt_work_handler() leader selection to use a local
  follower_mask copy instead of modifying the global rmpopt_cpumask.
  This eliminates the current_cpu_cleared tracking and the restore at
  the end, and removes the need for synchronization comments about
  transient cpumask inconsistency.
- Add three-way leader selection in rmpopt_work_handler():
  1. Current CPU is a primary thread in cpumask: run leader locally.
  2. Current CPU is a sibling thread whose primary is in cpumask:
     run leader locally (RMPOPT_BASE MSR is per-core), remove the
     primary from followers via cpumask_andnot(topology_sibling_cpumask).
  3. Current CPU's core has no RMPOPT_BASE MSR programmed: pick an
     explicit leader via cpumask_first() + smp_call_function_single()
     to avoid #UD, with cpus_read_lock() around the IPI loop.
- Add WARN_ON_ONCE guard for empty cpumask in the explicit leader
  fallback path, with migrate_enable() before goto out.
- Add .llseek = seq_lseek to rmpopt_table_fops for consistency with
  other seq_file-based debugfs files and to support tools like "less".
- Change debugfs file permissions from 0444 to 0400 to restrict access
  to root only.
- Add comment in rmpopt_table_seq_show() explaining why cpu_online_mask
  is safe: RMPOPT_BASE MSR is per-core and snp_prepare() ensures all
  CPUs are online when the MSR is programmed.

  Sashiko AI code review identified several of the above issues.

v5:
- Introduce rmpopt_cleanup() to tear down workqueue, debugfs, cpumask,
  and MSR state, called from snp_shutdown().
- Introduce rmpopt_wq_mutex to serialize snp_setup_rmpopt(),
  snp_rmpopt_all_physmem(), and rmpopt_cleanup().
- Introduce rmpopt_show_mutex to serialize debugfs reporting of
  rmpopt_report_cpumask.
- Move snp_rmpopt_all_physmem() call after SNP DECOMMISSION during
  guest shutdown.
- Use migrate_disable()/migrate_enable() for CPU pinning in the
  rmpopt_work_handler() leader loop to maintain CPU affinity without
  disabling preemption for the entire RMPOPT scan.
- Add cpus_read_lock()/cpus_read_unlock() around the follower
  on_each_cpu_mask() loop in rmpopt_work_handler().
- Guard snp_setup_rmpopt() against re-initialization when
  SNP_SHUTDOWN_EX with x86_snp_shutdown=0 skips rmpopt_cleanup()
  but clears snp_initialized, preventing workqueue and resource
  leaks on repeated init/shutdown cycles.
- Replace setup_clear_cpu_cap() with pr_err() on alloc_workqueue()
  failure in snp_setup_rmpopt(), as setup_clear_cpu_cap() cannot be
  used after alternatives are patched; callers check rmpopt_wq != NULL
  as the runtime guard instead.
- Add pr_info() when RMPOPT coverage is capped at 2TB.
- Add comments noting CPU hotplug is not supported with SNP enabled
  and only online primary threads are covered by rmpopt_cpumask.
- Add comment in setup_rmptable() noting Segmented RMP must be
  enabled to enable RMPOPT.
- Simplify cpumask setup loop to set if primary thread rather than
  skip if not primary.
- Improve grammar and clarity in snp_setup_rmpopt() comments.
- Added Reviewed-by's.

  Sashiko AI code review identified several of the above issues.

v4:
- Add new wrmsrq_on_cpus() helper to write same u64 value to a
  per-CPU MSR across a cpumask without per-cpu struct allocation
  overhead.
- Rename configure_and_enable_rmpopt() to snp_setup_rmpopt().
- Use wrmsrq_on_cpus() instead of wrmsrq_on_cpu() loop for
  programming RMPOPT_BASE MSRs.
- Add setup_clear_cpu_cap(X86_FEATURE_RMPOPT) if segmented RMP
  setup fails or workqueue allocation fails.
- Add X86_FEATURE_RMPOPT feature clear logic in amd_cc_platform_clear()
  for CC_ATTR_HOST_SEV_SNP.
- All of the above allow checking for only X86_FEATURE_RMPOPT for both
  RMPOPT setup/enable and RMP re-optimizations.
- Rename snp_perform_rmp_optimization() to snp_rmpopt_all_physmem().
- Split rmpopt() into rmpopt() and rmpopt_smp() for SMP callback use.
- Introduce separate rmpopt_report_cpumask for debugfs reporting,
  distinct from rmpopt_cpumask used for primary thread tracking.
- Remove snp_perform_rmp_optimization() call from __sev_snp_init_locked()
  and instead setup and enable RMPOPT after SNP is enabled and
  initialized.

v3:
- Drop all RMPOPT kthread support and introduce adding custom and
  dedicated workqueue to schedule delayed and asynchronous RMPOPT work.
- Drop the guest_memfd inode cleanup interface and add support to
  re-enable RMP optimizations during guest shutdown using the
  asynchronous and delayed workqueue interface.
- Introduce new __rmpopt() helper and rmpopt() and
  rmpopt_report_status() wrappers on top which use rax and rcx
  parameters to closely match RMPOPT specs.
- Use new optimized RMPOPT loop to issue RMPOPT instructions on all
  system RAM upto 2TB and all CPUs, by optimizing each range on one CPU
  first, then let other CPUs execute RMPOPT in parallel so they can skip
  most work as the range has already been optimized.
- Also add support for running the optimized RMPOPT loop only on
  one thread per core.
- Replace all PUD_SIZE references with SZ_1G to conform to 1GB regions
  as specified by RMPOPT specifications and not be dependent on PUD_SIZE
  which makes the RMPOPT patch-set independent of x86 page table sizes.
- Use wrmsrq_on_cpu() to program the RMPOPT_BASE MSR registers on
  all CPUs that removes all ugly casting to use on_each_cpu_mask().
- Fix inline commits and patch commit messages


v2:
- Drop all NUMA and Socket configuration and enablement support and
  enable RMPOPT support for up to 2TB of system RAM.
- Drop get_cpumask_of_primary_threads() and enable per-core RMPOPT
  base MSRs and issue RMPOPT instruction on all CPUs.
- Drop the configfs interface to manually re-enable RMP optimizations.
- Add new guest_memfd cleanup interface to automatically re-enable
  RMP optimizations during guest shutdown.
- Include references to the public RMPOPT documentation.
- Move debugfs directory for RMPOPT under architecuture specific
  parent directory.

Ashish Kalra (5):
  x86/cpufeatures: Add X86_FEATURE_RMPOPT feature flag
  x86/sev: Disable CPU hotplug while SNP is active
  x86/sev: Initialize RMPOPT configuration MSRs
  x86/sev: Perform RMP optimizations asynchronously
  x86/sev: Re-enable RMP optimizations on SNP guest shutdown

 arch/x86/include/asm/cpufeatures.h |   2 +-
 arch/x86/include/asm/msr-index.h   |   3 +
 arch/x86/include/asm/sev.h         |   2 +
 arch/x86/kernel/cpu/scattered.c    |   1 +
 arch/x86/kvm/svm/sev.c             |   2 +
 arch/x86/virt/svm/sev.c            | 193 ++++++++++++++++++++++++++---
 drivers/crypto/ccp/sev-dev.c       |   2 +
 7 files changed, 189 insertions(+), 16 deletions(-)

-- 
2.43.0

[PATCH v16 1/5] x86/cpufeatures: Add X86_FEATURE_RMPOPT feature flag

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

Add a flag indicating whether RMPOPT instruction is supported.

RMPOPT is a new instruction that reduces the performance overhead of RMP
checks for the hypervisor and non-SNP guests by allowing those checks to be
skipped when 1-GB memory regions are known to contain no SEV-SNP guest memory.

For more information on the RMPOPT instruction, see the AMD64 RMPOPT
technical documentation.

  [ bp: Zap respective tools/ change. ]

Suggested-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Link: https://patch.msgid.link/39e9ee269a572c516a3f4e937bfe12d00697d5e6.1782841284.git.ashish.kalra@amd.com
---
 arch/x86/include/asm/cpufeatures.h | 2 +-
 arch/x86/kernel/cpu/scattered.c    | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index f70ee74b5f92..3b5b32d3391b 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -76,7 +76,7 @@
 #define X86_FEATURE_K8			( 3*32+ 4) /* Opteron, Athlon64 */
 #define X86_FEATURE_ZEN5		( 3*32+ 5) /* CPU based on Zen5 microarchitecture */
 #define X86_FEATURE_ZEN6		( 3*32+ 6) /* CPU based on Zen6 microarchitecture */
-/* Free                                 ( 3*32+ 7) */
+#define X86_FEATURE_RMPOPT		( 3*32+ 7) /* Support for AMD RMPOPT instruction */
 #define X86_FEATURE_CONSTANT_TSC	( 3*32+ 8) /* "constant_tsc" TSC ticks at a constant rate */
 /* free: was #define X86_FEATURE_UP	( 3*32+ 9) * "up" SMP kernel running on UP */
 #define X86_FEATURE_ART			( 3*32+10) /* "art" Always running timer (ART) */
diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index 8665a6474806..d1795ce219da 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -67,6 +67,7 @@ static const struct cpuid_bit cpuid_bits[] = {
 	{ X86_FEATURE_PERFMON_V2,		CPUID_EAX,  0, 0x80000022, 0 },
 	{ X86_FEATURE_AMD_LBR_V2,		CPUID_EAX,  1, 0x80000022, 0 },
 	{ X86_FEATURE_AMD_LBR_PMC_FREEZE,	CPUID_EAX,  2, 0x80000022, 0 },
+	{ X86_FEATURE_RMPOPT,			CPUID_EDX,  0, 0x80000025, 0 },
 	{ X86_FEATURE_AMD_HTR_CORES,		CPUID_EAX, 30, 0x80000026, 0 },
 	{ 0, 0, 0, 0, 0 }
 };
-- 
2.43.0

[PATCH v16 2/5] x86/sev: Disable CPU hotplug while SNP is active

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

While SNP is active, every memory write is checked against the RMP to
protect SNP guest memory.  A core performs these RMP checks only once
SNP has been initialized via SNP_INIT and the SNP-enable bit in SYSCFG is
set on that core; the firmware requires the SNP-enable bit to be set on
every present CPU before SNP initialization.

A core that is not SNP-enabled and not SNP-initialized performs no RMP
checks at all, so there is no valid configuration with SNP active and any
CPU exempt from RMP checks.

The firmware determines which CPUs are present from the processor and the
BIOS/UEFI configuration (e.g. SMT disabled in the BIOS) and enumerates
them at SNP init; it is not aware of the OS bringing CPUs online or
offline afterwards.

SNP_INIT fails unless SnpEn is set on all CPUs, so a CPU that is offline
when SNP_INIT is issued, does not have SnpEn set, SNP_INIT fails, and
there can be no SNP guest memory.  OS CPU hotplug can thus diverge from
the firmware's expectations and break SNP.

Tie CPU hotplug to the SNP-enable bit: disable it in snp_prepare() before
SNP is enabled, and re-enable it in snp_shutdown() once the firmware has
disabled SNP.

If snp_prepare() fails before enabling SNP it re-enables hotplug itself;
once SNP is enabled hotplug stays disabled, including across a failed
SNP_INIT and across the legacy SNP_SHUTDOWN_EX path, both of which leave
SNP enabled.

A kexec target that boots with SNP already enabled, disables hotplug once
in snp_rmptable_init(), since snp_prepare() bails when SNP is already
enabled.

With CPU hotplug now disabled while SNP is active, the online CPU mask is
stable, so the cpus_read_lock() previously taken in snp_prepare() to
iterate it is redundant.  Drop cpus_read_lock()/cpus_read_unlock() here.

Suggested-by: Thomas Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
 arch/x86/virt/svm/sev.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index cff285d8ad8e..558f7924a3f8 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -513,7 +513,6 @@ static void clear_hsave_pa(void *arg)
 
 int snp_prepare(void)
 {
-	int ret;
 	u64 val;
 
 	/*
@@ -526,14 +525,18 @@ int snp_prepare(void)
 
 	clear_rmp();
 
-	cpus_read_lock();
+	/*
+	 * No CPU may come online without SnpEn while SNP is active; disable
+	 * hotplug here and re-enable it in snp_shutdown().
+	 */
+	cpu_hotplug_disable();
 
 	if (!cpumask_equal(cpu_online_mask, cpu_present_mask)) {
-		ret = -EOPNOTSUPP;
+		cpu_hotplug_enable();
 		pr_warn("SNP init failed: not all CPUs online. (%*pbl online <-> %*pbl present masks).\n",
 			cpumask_pr_args(cpu_online_mask),
 			cpumask_pr_args(cpu_present_mask));
-		goto unlock;
+		return -EOPNOTSUPP;
 	}
 
 	wbinvd_on_all_cpus();
@@ -548,12 +551,7 @@ int snp_prepare(void)
 	/* SNP_INIT requires MSR_VM_HSAVE_PA to be cleared on all CPUs. */
 	on_each_cpu(clear_hsave_pa, NULL, 1);
 
-	ret = 0;
-
-unlock:
-	cpus_read_unlock();
-
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_prepare, "ccp");
 
@@ -567,6 +565,13 @@ void snp_shutdown(void)
 
 	clear_rmp();
 	on_each_cpu(mfd_reconfigure, NULL, 1);
+
+	/*
+	 * The firmware has disabled SNP (SnpEn is clear), so re-enable CPU
+	 * hotplug.  A legacy SNP shutdown returns above with SnpEn still set and
+	 * leaves hotplug disabled.
+	 */
+	cpu_hotplug_enable();
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
 
@@ -577,6 +582,8 @@ EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
  */
 int __init snp_rmptable_init(void)
 {
+	u64 val;
+
 	if (WARN_ON_ONCE(!cc_platform_has(CC_ATTR_HOST_SEV_SNP)))
 		return -ENOSYS;
 
@@ -586,6 +593,15 @@ int __init snp_rmptable_init(void)
 	if (!setup_rmptable())
 		return -ENOSYS;
 
+	/*
+	 * On a kexec boot SNP may already be enabled (legacy firmware leaves
+	 * SnpEn set across shutdown), in which case snp_prepare() bails without
+	 * disabling CPU hotplug, so disable it here.
+	 */
+	rdmsrq(MSR_AMD64_SYSCFG, val);
+	if (val & MSR_AMD64_SYSCFG_SNP_EN)
+		cpu_hotplug_disable();
+
 	/*
 	 * Setting crash_kexec_post_notifiers to 'true' to ensure that SNP panic
 	 * notifier is invoked to do SNP IOMMU shutdown before kdump.
-- 
2.43.0

[PATCH v16 3/5] x86/sev: Initialize RMPOPT configuration MSRs

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

The new RMPOPT instruction helps manage per-CPU RMP optimization
structures inside the CPU. It takes a 1GB-aligned physical address
and either returns the status of the optimizations or tries to enable
the optimizations.

Per-CPU RMPOPT tables support at most 2 TB of addressable memory for
RMP optimizations.

Initialize the per-CPU RMPOPT table base to the starting physical
address. This enables RMP optimization for up to 2 TB of system RAM on
all CPUs.

Add snp_enable_rmpopt() to program RMPOPT once SNP is enabled and
initialized.

Suggested-by: Thomas Lendacky <thomas.lendacky@amd.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
Changes in v16:
- Clear X86_FEATURE_RMPOPT when segmented RMP is enabled but its probe
  fails, so the initcall does not set up RMPOPT for a system that will not
  bring up SNP.
- Program the RMPOPT_BASE MSRs (with wrmsrq_on_cpu()) only when RMPOPT_EN is
  not already set on the local CPU, so guest teardown skips reprogramming
  instead of reprogramming the MSRs on every teardown.

Changes in v15:
- Rename snp_setup_rmpopt() to snp_enable_rmpopt().
- Program each core's RMPOPT_BASE only when it is not already set.
 arch/x86/include/asm/msr-index.h |  3 ++
 arch/x86/include/asm/sev.h       |  2 +
 arch/x86/virt/svm/sev.c          | 66 +++++++++++++++++++++++++++++---
 drivers/crypto/ccp/sev-dev.c     |  2 +
 4 files changed, 68 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 3a8e51a0c9e8..1635e2e1c576 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -761,6 +761,9 @@
 #define MSR_AMD64_SEG_RMP_ENABLED_BIT	0
 #define MSR_AMD64_SEG_RMP_ENABLED	BIT_ULL(MSR_AMD64_SEG_RMP_ENABLED_BIT)
 #define MSR_AMD64_RMP_SEGMENT_SHIFT(x)	(((x) & GENMASK_ULL(13, 8)) >> 8)
+#define MSR_AMD64_RMPOPT_BASE		0xc0010139
+#define MSR_AMD64_RMPOPT_ENABLE_BIT	0
+#define MSR_AMD64_RMPOPT_ENABLE		BIT_ULL(MSR_AMD64_RMPOPT_ENABLE_BIT)
 
 #define MSR_SVSM_CAA			0xc001f000
 
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 9e7a077c445d..fa81aa004e8b 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -662,6 +662,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int pages)
 	__snp_leak_pages(pfn, pages, true);
 }
 int snp_prepare(void);
+void snp_enable_rmpopt(void);
 void snp_shutdown(void);
 #else
 static inline bool snp_probe_rmptable_info(void) { return false; }
@@ -680,6 +681,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
 static inline void kdump_sev_callback(void) { }
 static inline void snp_fixup_e820_tables(void) {}
 static inline int snp_prepare(void) { return -ENODEV; }
+static inline void snp_enable_rmpopt(void) {}
 static inline void snp_shutdown(void) {}
 #endif
 
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 558f7924a3f8..25cb486ff61b 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -124,6 +124,8 @@ static void *rmp_bookkeeping __ro_after_init;
 
 static u64 probed_rmp_base, probed_rmp_size;
 
+static phys_addr_t rmpopt_pa_start;
+
 static LIST_HEAD(snp_leaked_pages_list);
 static DEFINE_SPINLOCK(snp_leaked_pages_list_lock);
 
@@ -575,6 +577,42 @@ void snp_shutdown(void)
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
 
+static bool rmpopt_capable(void)
+{
+	return cpu_feature_enabled(X86_FEATURE_RMPOPT) &&
+	       cc_platform_has(CC_ATTR_HOST_SEV_SNP);
+}
+
+void snp_enable_rmpopt(void)
+{
+	u64 base;
+	int cpu;
+
+	if (!rmpopt_capable())
+		return;
+
+	rmpopt_pa_start = ALIGN_DOWN(PFN_PHYS(min_low_pfn), SZ_1G);
+
+	/*
+	 * Per-CPU RMPOPT tables cover at most 2 TB.  Program each core's
+	 * RMPOPT_BASE with the start of RAM to optimize up to 2 TB.  The MSR
+	 * can only be written after SNP is enabled, so this runs from the ccp
+	 * SNP init path (and again on guest teardown) rather than an initcall.
+	 *
+	 * The loop below programs RMPOPT_BASE on all primary threads.  RMPOPT_EN
+	 * cannot be cleared while SNP is enabled, and CPU hotplug is disabled
+	 * while SNP is active, so once programmed the MSRs stay set on all CPUs
+	 * until SNP is disabled.  A set RMPOPT_EN on the local CPU therefore
+	 * means the programming has already been done, so skip it.
+	 */
+	rdmsrq(MSR_AMD64_RMPOPT_BASE, base);
+	if (!(base & MSR_AMD64_RMPOPT_ENABLE))
+		for_each_cpu(cpu, cpu_primary_thread_mask)
+			wrmsrq_on_cpu(cpu, MSR_AMD64_RMPOPT_BASE,
+				      rmpopt_pa_start | MSR_AMD64_RMPOPT_ENABLE);
+}
+EXPORT_SYMBOL_FOR_MODULES(snp_enable_rmpopt, "ccp");
+
 /*
  * Do the necessary preparations which are verified by the firmware as
  * described in the SNP_INIT_EX firmware command description in the SNP
@@ -699,13 +737,31 @@ static bool probe_segmented_rmptable_info(void)
 
 bool snp_probe_rmptable_info(void)
 {
-	if (cpu_feature_enabled(X86_FEATURE_SEGMENTED_RMP))
+	if (cpu_feature_enabled(X86_FEATURE_SEGMENTED_RMP)) {
 		rdmsrq(MSR_AMD64_RMP_CFG, rmp_cfg);
 
-	if (rmp_cfg & MSR_AMD64_SEG_RMP_ENABLED)
-		return probe_segmented_rmptable_info();
-	else
-		return probe_contiguous_rmptable_info();
+		if (rmp_cfg & MSR_AMD64_SEG_RMP_ENABLED) {
+			if (probe_segmented_rmptable_info())
+				return true;
+
+			/*
+			 * Segmented RMP is enabled but misconfigured; RMPOPT is
+			 * unusable, so drop the capability before it reaches the
+			 * initcall.
+			 */
+			setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
+			return false;
+		}
+	}
+
+	/*
+	 * Segmented RMP is either not supported on the platform or is
+	 * disabled by the firmware.  RMPOPT is not supported without
+	 * segmented RMP.
+	 */
+	setup_clear_cpu_cap(X86_FEATURE_RMPOPT);
+
+	return probe_contiguous_rmptable_info();
 }
 
 /*
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index f833cb7e4da3..5c996ab63895 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1663,6 +1663,8 @@ static int __sev_snp_init_locked(int *error, unsigned int max_snp_asid)
 
 	sev_es_tmr_size = SNP_TMR_SIZE;
 
+	snp_enable_rmpopt();
+
 	return 0;
 }
 
-- 
2.43.0

[PATCH v16 4/5] x86/sev: Perform RMP optimizations asynchronously

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

When SNP is enabled, all writes to memory are checked to ensure memory
integrity. This imposes performance overhead on the whole system.

RMPOPT is a new instruction that minimizes the performance overhead of
RMP checks on the hypervisor and on non-SNP guests by allowing RMP
checks to be skipped for 1GB regions of memory that are known not to
contain any SNP guest memory.

Add support for performing RMP optimizations asynchronously using a
dedicated per-CPU workqueue. The workqueue is allocated from an initcall,
and snp_enable_rmpopt() queues the optimization pass.

Shortly after SNP initialization, run an optimization pass over all
physical memory (up to 2TB of system RAM, starting from the lowest
physical memory address aligned down to a 1GB boundary), skipping RMP
checks for 1GB regions that do not contain SNP guest memory (excluding
preassigned pages such as the RMP table and firmware pages).

As SNP guests are launched, RMPUPDATE assigns their private pages to
guest-owned state; when such a page falls within an optimized 1GB
region, the hardware clears that region's RMPOPT optimization and RMP
checks resume there to protect the guest memory.

Since launching SNP guests clears these optimizations, perform them
again asynchronously using the dedicated workqueue.

Suggested-by: Thomas Lendacky <thomas.lendacky@amd.com>
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
Changes in v15:
- Move the workqueue allocation and the (fixed) optimization range
  computation to an initcall; snp_enable_rmpopt() now only programs the
  RMPOPT_BASE MSRs and queues the optimization pass.
- Gate rmpopt_capable() on a static rmpopt_enabled bool set when the
  workqueue is allocated, instead of an if (rmpopt_wq) check, and drop
  rmpopt_wq_mutex.
- Queue both the initial and the teardown pass with mod_delayed_work().
 arch/x86/virt/svm/sev.c | 99 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 95 insertions(+), 4 deletions(-)

diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 25cb486ff61b..bd97135cacc2 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -19,6 +19,7 @@
 #include <linux/iommu.h>
 #include <linux/amd-iommu.h>
 #include <linux/nospec.h>
+#include <linux/workqueue.h>
 
 #include <asm/sev.h>
 #include <asm/processor.h>
@@ -124,7 +125,25 @@ static void *rmp_bookkeeping __ro_after_init;
 
 static u64 probed_rmp_base, probed_rmp_size;
 
-static phys_addr_t rmpopt_pa_start;
+static u64 rmpopt_pa_start, rmpopt_pa_end;
+
+enum rmpopt_op_type {
+	RMPOPT_OP_VERIFY_AND_REPORT_STATUS,
+	RMPOPT_OP_REPORT_STATUS
+};
+
+static struct workqueue_struct *rmpopt_wq;
+static struct delayed_work rmpopt_delayed_work;
+static bool rmpopt_enabled;
+
+/*
+ * Delay, in milliseconds, before the RMP re-optimization pass runs after an SNP
+ * guest is torn down, passed as the delay to mod_delayed_work().  This coalesces
+ * a burst of teardowns into a single scan and gives each guest's pages time to
+ * be converted back to the shared, hypervisor-owned state.  The 10 second value
+ * is a heuristic trading re-optimization latency against scanning too eagerly.
+ */
+#define RMPOPT_WORK_TIMEOUT	(10 * MSEC_PER_SEC)
 
 static LIST_HEAD(snp_leaked_pages_list);
 static DEFINE_SPINLOCK(snp_leaked_pages_list_lock);
@@ -557,6 +576,12 @@ int snp_prepare(void)
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_prepare, "ccp");
 
+static void rmpopt_disable(void)
+{
+	if (rmpopt_wq)
+		cancel_delayed_work_sync(&rmpopt_delayed_work);
+}
+
 void snp_shutdown(void)
 {
 	u64 syscfg;
@@ -565,6 +590,8 @@ void snp_shutdown(void)
 	if (syscfg & MSR_AMD64_SYSCFG_SNP_EN)
 		return;
 
+	rmpopt_disable();
+
 	clear_rmp();
 	on_each_cpu(mfd_reconfigure, NULL, 1);
 
@@ -580,8 +607,69 @@ EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
 static bool rmpopt_capable(void)
 {
 	return cpu_feature_enabled(X86_FEATURE_RMPOPT) &&
-	       cc_platform_has(CC_ATTR_HOST_SEV_SNP);
+	       cc_platform_has(CC_ATTR_HOST_SEV_SNP) && rmpopt_enabled;
+}
+
+/*
+ * RMPOPT optimizations skip RMP checks at 1GB granularity if this range of
+ * memory does not contain any SNP guest memory.
+ *
+ * @pa is a system physical address; RMPOPT operates on the containing 1GB.
+ */
+static void rmpopt(u64 pa)
+{
+	enum rmpopt_op_type op = RMPOPT_OP_VERIFY_AND_REPORT_STATUS;
+	u64 pa_start = ALIGN_DOWN(pa, SZ_1G);
+
+	/* Supported by binutils 2.48+ */
+	asm volatile(".byte 0xf2, 0x0f, 0x01, 0xfc"
+		     :: "a" (pa_start), "c" (op)
+		     : "memory", "cc");
+}
+
+static void rmpopt_scan_range(void *arg)
+{
+	u64 pa;
+
+	for (pa = rmpopt_pa_start; pa < rmpopt_pa_end; pa += SZ_1G)
+		rmpopt(pa);
+}
+
+static void do_rmpopt_work(struct work_struct *work)
+{
+	/*
+	 * Warm up the RMPOPT cache on this pinned per-CPU worker with interrupts
+	 * enabled, so the IRQ-disabled fan-out below only issues cache-hit RMPOPTs.
+	 */
+	rmpopt_scan_range(NULL);
+
+	on_each_cpu_mask(cpu_primary_thread_mask, rmpopt_scan_range, NULL, true);
+}
+
+static int __init rmpopt_init(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_RMPOPT))
+		return 0;
+
+	rmpopt_wq = alloc_workqueue("rmpopt_wq", WQ_PERCPU, 1);
+	if (!rmpopt_wq) {
+		pr_err("Failed to allocate RMPOPT workqueue\n");
+		return 0;
+	}
+
+	INIT_DELAYED_WORK(&rmpopt_delayed_work, do_rmpopt_work);
+
+	/* The optimization range is fixed at boot; compute it once. */
+	rmpopt_pa_start = ALIGN_DOWN(PFN_PHYS(min_low_pfn), SZ_1G);
+	rmpopt_pa_end = ALIGN(PFN_PHYS(max_pfn), SZ_1G);
+	if ((rmpopt_pa_end - rmpopt_pa_start) > SZ_2T)
+		rmpopt_pa_end = rmpopt_pa_start + SZ_2T;
+
+	rmpopt_enabled = true;
+
+	return 0;
 }
+device_initcall(rmpopt_init);
 
 void snp_enable_rmpopt(void)
 {
@@ -591,8 +679,6 @@ void snp_enable_rmpopt(void)
 	if (!rmpopt_capable())
 		return;
 
-	rmpopt_pa_start = ALIGN_DOWN(PFN_PHYS(min_low_pfn), SZ_1G);
-
 	/*
 	 * Per-CPU RMPOPT tables cover at most 2 TB.  Program each core's
 	 * RMPOPT_BASE with the start of RAM to optimize up to 2 TB.  The MSR
@@ -610,6 +696,11 @@ void snp_enable_rmpopt(void)
 		for_each_cpu(cpu, cpu_primary_thread_mask)
 			wrmsrq_on_cpu(cpu, MSR_AMD64_RMPOPT_BASE,
 				      rmpopt_pa_start | MSR_AMD64_RMPOPT_ENABLE);
+
+	mod_delayed_work(rmpopt_wq, &rmpopt_delayed_work,
+			 msecs_to_jiffies(RMPOPT_WORK_TIMEOUT));
+
+	pr_info_once("RMPOPT optimizations enabled\n");
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_enable_rmpopt, "ccp");
 
-- 
2.43.0

[PATCH v16 5/5] x86/sev: Re-enable RMP optimizations on SNP guest shutdown

[Ashish Kalra]

From: Ashish Kalra <ashish.kalra@amd.com>

The RMPOPT table is a per-CPU table which indicates whether 1GB regions
of physical memory are entirely hypervisor-owned.

When performing host memory accesses in hypervisor mode as well as
non-SNP guest mode, the processor may consult the RMPOPT table to
potentially skip an RMP access and improve performance.

Normal guest events disable RMP optimizations: pages are converted from
shared to private as SNP guests are launched, and large pages are split
and collapsed during guest operation -- both disable the RMPOPT
optimizations for the affected 1GB regions.

When guests are torn down, their pages are converted back to shared, so
those regions may become eligible for RMPOPT optimization again. Without
some intervention, all RMP optimizations would eventually be lost, so
re-optimize all of physical memory on SNP guest teardown by calling
snp_enable_rmpopt().

snp_enable_rmpopt() performs the re-optimization after a delay, using
mod_delayed_work() so that the delay timer is reset on each call. This
batches multiple guest terminations into a single pass: the
re-optimization runs 10 seconds after the *last* termination rather than
after the first. mod_delayed_work() also re-queues work that is already
in-flight, so a re-scan request during an active scan is not silently
dropped.

Guest teardown is currently the only event that returns guest memory to
hypervisor ownership: SNP guests do not support ballooning or memory
hotplug, so pages freed during a guest's lifetime remain guest-owned.
It is therefore the only point at which memory becomes eligible for RMP
re-optimization, which is why re-optimization is driven by guest
teardown rather than by a periodic scan.

Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
Changes in v15:
- Call snp_enable_rmpopt() on guest teardown instead of a separate
  snp_rmpopt_all_physmem(); the delayed re-optimization now lives in
  snp_enable_rmpopt().
 arch/x86/kvm/svm/sev.c  | 2 ++
 arch/x86/virt/svm/sev.c | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 5705723f1f41..4d5e30af1ade 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3032,6 +3032,8 @@ void sev_vm_destroy(struct kvm *kvm)
 		 */
 		if (snp_decommission_context(kvm))
 			return;
+
+		snp_enable_rmpopt();
 	} else {
 		sev_unbind_asid(kvm, sev->handle);
 	}
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index bd97135cacc2..13d9acb319aa 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -702,7 +702,7 @@ void snp_enable_rmpopt(void)
 
 	pr_info_once("RMPOPT optimizations enabled\n");
 }
-EXPORT_SYMBOL_FOR_MODULES(snp_enable_rmpopt, "ccp");
+EXPORT_SYMBOL_FOR_MODULES(snp_enable_rmpopt, "ccp,kvm-amd");
 
 /*
  * Do the necessary preparations which are verified by the firmware as
-- 
2.43.0

Re: [PATCH v16 2/5] x86/sev: Disable CPU hotplug while SNP is active

[Borislav Petkov]

On Wed, Sep 16, 2026 at 10:36:30PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] x86/sev: CPU hotplug disablement bypassed on early kexec errors
> --
> 
> commit ac084f2d7188c520f2ee3ced2ab76e4c068df91f
> Author: Ashish Kalra <ashish.kalra@amd.com>
> 
> x86/sev: Disable CPU hotplug while SNP is active
> 
> This commit disables CPU hotplug when SNP is enabled to prevent SNP guest
> memory from being broken by CPUs coming online without the SnpEn bit set.
> It ties CPU hotplug to the SNP-enable bit, disabling it in snp_prepare()
> and re-enabling it in snp_shutdown() when SNP is disabled. It also
> explicitly disables CPU hotplug during kexec if SNP is already enabled.
> 
> > diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> > index cff285d8ad8e3..558f7924a3f85 100644
> > --- a/arch/x86/virt/svm/sev.c
> > +++ b/arch/x86/virt/svm/sev.c
> 
> [ ... ]
> 
> > @@ -577,6 +582,8 @@ EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
> >   */
> >  int __init snp_rmptable_init(void)
> >  {
> > +	u64 val;
> > +
> >  	if (WARN_ON_ONCE(!cc_platform_has(CC_ATTR_HOST_SEV_SNP)))
> >  		return -ENOSYS;
> >  
> > @@ -586,6 +593,15 @@ int __init snp_rmptable_init(void)
> >  	if (!setup_rmptable())
> >  		return -ENOSYS;
> >  
> > +	/*
> > +	 * On a kexec boot SNP may already be enabled (legacy firmware leaves
> > +	 * SnpEn set across shutdown), in which case snp_prepare() bails without
> > +	 * disabling CPU hotplug, so disable it here.
> > +	 */
> > +	rdmsrq(MSR_AMD64_SYSCFG, val);
> > +	if (val & MSR_AMD64_SYSCFG_SNP_EN)
> > +		cpu_hotplug_disable();
> 
> [Severity: High]
> If a kexec kernel boots into a system where the previous kernel left
> MSR_AMD64_SYSCFG_SNP_EN active, and an early initialization step fails
> (such as passing amd_iommu=off

amd_iommu=off means no SNP.

> on the kernel command line resulting in !amd_iommu_snp_en, or
> setup_rmptable() failing),

The same happens in that case:

        if (snp_rmptable_init()) {
                pr_warn("SNP: RMP initialization failed, SNP cannot be supported.\n");
                goto disable_snp;
		     ^^^^^^^^^^^

Does Sashiko not see that or somehow it ate a lot of credits so it cannot use
enough now to "swap in" the whole context... if that is the AI that is going
to destroy the world, then I'm not too worried. :)

Or is my AI failing me right now?

:-P

Leaving in the rest.

> snp_rmptable_init() will
> return -ENOSYS before checking the physical MSR hardware state and
> disabling CPU hotplug.
> 
> Because hotplug remains enabled and the CCP driver skips initialization on
> failure (bypassing snp_prepare()), could a subsequently hotplugged CPU come
> online without the SNP_EN bit set?

Yes, but the above disabled all our intention of running SNP in the first
place...
 
> If this results in a mixed hardware state, does it violate firmware
> constraints and cause fatal RMP faults when the new CPU accesses memory?
> 
> Should the hardware state be checked and hotplug disabled unconditionally
> before the software configuration checks?
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/cover.1789594774.git.ashish.kalra@amd.com?part=2

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v16 2/5] x86/sev: Disable CPU hotplug while SNP is active

[Kalra, Ashish]

Hello Boris,

On 9/16/2026 9:19 PM, Borislav Petkov wrote:
> On Wed, Sep 16, 2026 at 10:36:30PM +0000, sashiko-bot@kernel.org wrote:
>> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
>> - [High] x86/sev: CPU hotplug disablement bypassed on early kexec errors
>> --
>>
>> commit ac084f2d7188c520f2ee3ced2ab76e4c068df91f
>> Author: Ashish Kalra <ashish.kalra@amd.com>
>>
>> x86/sev: Disable CPU hotplug while SNP is active
>>
>> This commit disables CPU hotplug when SNP is enabled to prevent SNP guest
>> memory from being broken by CPUs coming online without the SnpEn bit set.
>> It ties CPU hotplug to the SNP-enable bit, disabling it in snp_prepare()
>> and re-enabling it in snp_shutdown() when SNP is disabled. It also
>> explicitly disables CPU hotplug during kexec if SNP is already enabled.
>>
>>> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
>>> index cff285d8ad8e3..558f7924a3f85 100644
>>> --- a/arch/x86/virt/svm/sev.c
>>> +++ b/arch/x86/virt/svm/sev.c
>>
>> [ ... ]
>>
>>> @@ -577,6 +582,8 @@ EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
>>>   */
>>>  int __init snp_rmptable_init(void)
>>>  {
>>> +	u64 val;
>>> +
>>>  	if (WARN_ON_ONCE(!cc_platform_has(CC_ATTR_HOST_SEV_SNP)))
>>>  		return -ENOSYS;
>>>  
>>> @@ -586,6 +593,15 @@ int __init snp_rmptable_init(void)
>>>  	if (!setup_rmptable())
>>>  		return -ENOSYS;
>>>  
>>> +	/*
>>> +	 * On a kexec boot SNP may already be enabled (legacy firmware leaves
>>> +	 * SnpEn set across shutdown), in which case snp_prepare() bails without
>>> +	 * disabling CPU hotplug, so disable it here.
>>> +	 */
>>> +	rdmsrq(MSR_AMD64_SYSCFG, val);
>>> +	if (val & MSR_AMD64_SYSCFG_SNP_EN)
>>> +		cpu_hotplug_disable();
>>
>> [Severity: High]
>> If a kexec kernel boots into a system where the previous kernel left
>> MSR_AMD64_SYSCFG_SNP_EN active, and an early initialization step fails
>> (such as passing amd_iommu=off
> 
> amd_iommu=off means no SNP.
> 
>> on the kernel command line resulting in !amd_iommu_snp_en, or
>> setup_rmptable() failing),
> 
> The same happens in that case:
> 
>         if (snp_rmptable_init()) {
>                 pr_warn("SNP: RMP initialization failed, SNP cannot be supported.\n");
>                 goto disable_snp;
> 		     ^^^^^^^^^^^
> 
> Does Sashiko not see that or somehow it ate a lot of credits so it cannot use
> enough now to "swap in" the whole context... if that is the AI that is going
> to destroy the world, then I'm not too worried. :)
> 
> Or is my AI failing me right now?
> 
> :-P
> 
> Leaving in the rest.

Right, agreed — 

As you have pointed out, on any snp_rmptable_init() failure — setup_rmptable() failing,
!amd_iommu_snp_en (amd_iommu=off), etc. — the caller does goto disable_snp and SNP is
disabled entirely. 

Thanks,
Ashish

> 
>> snp_rmptable_init() will
>> return -ENOSYS before checking the physical MSR hardware state and
>> disabling CPU hotplug.
>>
>> Because hotplug remains enabled and the CCP driver skips initialization on
>> failure (bypassing snp_prepare()), could a subsequently hotplugged CPU come
>> online without the SNP_EN bit set?
> 
> Yes, but the above disabled all our intention of running SNP in the first
> place...
>  
>> If this results in a mixed hardware state, does it violate firmware
>> constraints and cause fatal RMP faults when the new CPU accesses memory?
>>
>> Should the hardware state be checked and hotplug disabled unconditionally
>> before the software configuration checks?
>>
>> -- 
>> Sashiko AI review · https://sashiko.dev/#/patchset/cover.1789594774.git.ashish.kalra@amd.com?part=2
>