[PATCH v2 0/3] KVM: PPC: Fixes for Book3S HV HPT locking and paired-single decoding

[Amit Machhiwal <amachhiw@linux.ibm.com>]

This series addresses bug fixes across KVM PPC Book3S HV
locking/synchronization and paired-single instruction decoding.

Patches 1 & 2 fix synchronization and preemption issues introduced in
commit 6165d5dd99db ("KVM: PPC: Book3S HV: add virtual mode handlers for
HPT hcalls and page faults"):

- Patch 1 adds SRCU read lock protection when walking memslots during
  virtual-mode HPT hcalls to prevent use-after-free races with concurrent
  memslot updates.

- Patch 2 adds preempt_disable() around all virtual-mode HPTE bit-lock
  holders — both the guest vCPU paths (kvmppc_hpte_hv_fault() and
  kvmppc_pseries_do_hpt_hcall()) and the host-side paths
  (kvm_unmap_rmapp(), kvm_age_rmapp(), kvm_test_clear_dirty_npages(),
  resize_hpt_rehash_hpte()) — to prevent CPU stalls and deadlocks on
  preemption.

Patch 3 fixes paired-single D-form instruction emulation:

- Patch 3 fixes get_d_signext() to correctly extract the full 12-bit D
  displacement field and perform proper two's-complement sign extension.

Testing:
========
All test kernel builds were compiled with CONFIG_DEBUG_ATOMIC_SLEEP=y.
The following scenarios were verified:

1. Power9 PowerNV (L0) in Radix mode:
   - Booted L0 host with kernel containing all 3 patches.
   - Booted KVM guests in both Radix and Hash modes.
   - Ran kernel build workload inside guests — no errors observed.
   - Booted L1 guest with the same kernel — booted and ran cleanly.

2. Power9 PowerNV (L0) in Hash mode:
   - Booted L0 host with kernel containing all 3 patches.
   - Booted KVM guest in Hash mode.
   - Ran kernel build workload inside guest — no errors observed.
   - Booted L1 nested guest with the same kernel — booted and ran cleanly.

3. Power10 LPAR (L1):
   - Booted Power10 LPAR with the patched kernel.
   - Booted KVM guest and ran workloads — no errors observed.

Changes in v2:
==============
- v1: https://lore.kernel.org/all/20260928122837.8782-1-amachhiw@linux.ibm.com/
- Patch 2: Extended preempt_disable()/preempt_enable() coverage to also wrap
  the HPTE bit-lock hold windows in four host-side virtual-mode functions:
  kvm_unmap_rmapp(), kvm_age_rmapp(), kvm_test_clear_dirty_npages(), and
  resize_hpt_rehash_hpte(). These were identified as vulnerable by Sashiko AI
  review and confirmed correct by audit.
- Dropped Reviewed-by from Ritesh as the patch was materially extended.
- Patch 2: Added warning comment above kvmppc_pseries_do_hpt_hcall()
  documenting the preemption requirement.

Amit Machhiwal (3):
  KVM: PPC: Book3S HV: Add SRCU protection for virtual-mode HPT hcalls
  KVM: PPC: Book3S HV: Add preempt_disable() around virtual-mode HPTE
    bit-lock users
  KVM: PPC: Fix get_d_signext() 12-bit displacement for paired-single
    D-form

 arch/powerpc/kvm/book3s_64_mmu_hv.c      | 12 ++++
 arch/powerpc/kvm/book3s_hv.c             | 80 +++++++++++++-----------
 arch/powerpc/kvm/book3s_paired_singles.c |  7 +--
 3 files changed, 58 insertions(+), 41 deletions(-)


base-commit: 551c722f40809618230001baccf219193e22fc5a
-- 
2.54.0 (Apple Git-157)