[PATCH] x86/CPU/AMD: don't force the CPB cap when running under a hypervisor

[PATCH] x86/CPU/AMD: don't force the CPB cap when running under a hypervisor

[Frank van der Linden]

For F17h AMD CPUs, the CPB capability is forcibly set, because some
versions of that chip incorrectly report that they do not have it.

However, a hypervisor may filter out the CPB capability, for good
reasons. For example, KVM currently does not emulate setting the CPB
bit in MSR_K7_HWCR, and unchecked MSR access errors will be thrown
when trying to set it as a guest:

	unchecked MSR access error: WRMSR to 0xc0010015 (tried to write
        0x0000000001000011) at rIP: 0xffffffff890638f4
        (native_write_msr+0x4/0x20)

	Call Trace:
	boost_set_msr+0x50/0x80 [acpi_cpufreq]
	cpuhp_invoke_callback+0x86/0x560
	sort_range+0x20/0x20
	cpuhp_thread_fun+0xb0/0x110
	smpboot_thread_fn+0xef/0x160
	kthread+0x113/0x130
	kthread_create_worker_on_cpu+0x70/0x70
	ret_from_fork+0x35/0x40

To avoid this issue, don't forcibly set the CPB capability for a CPU
when running under a hypervisor.

Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Fixes: 0237199186e7 ("x86/CPU/AMD: Set the CPB bit unconditionally on F17h")
---
 arch/x86/kernel/cpu/amd.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index fb6a64bd765f..ee4d79fa1b19 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -823,8 +823,11 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
 {
 	set_cpu_cap(c, X86_FEATURE_ZEN);
 
-	/* Fix erratum 1076: CPB feature bit not being set in CPUID. */
-	if (!cpu_has(c, X86_FEATURE_CPB))
+	/*
+	 * Fix erratum 1076: CPB feature bit not being set in CPUID.
+	 * Always set it, except when running under a hypervisor.
+	 */
+	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
 		set_cpu_cap(c, X86_FEATURE_CPB);
 }
 
-- 
2.17.2

Re: [PATCH] x86/CPU/AMD: don't force the CPB cap when running under a hypervisor

[Borislav Petkov]

On Wed, May 22, 2019 at 10:17:45PM +0000, Frank van der Linden wrote:
> For F17h AMD CPUs, the CPB capability is forcibly set, because some
> versions of that chip incorrectly report that they do not have it.
> 
> However, a hypervisor may filter out the CPB capability, for good
> reasons. For example, KVM currently does not emulate setting the CPB
> bit in MSR_K7_HWCR, and unchecked MSR access errors will be thrown
> when trying to set it as a guest:
> 
> 	unchecked MSR access error: WRMSR to 0xc0010015 (tried to write
>         0x0000000001000011) at rIP: 0xffffffff890638f4
>         (native_write_msr+0x4/0x20)
> 
> 	Call Trace:
> 	boost_set_msr+0x50/0x80 [acpi_cpufreq]
> 	cpuhp_invoke_callback+0x86/0x560
> 	sort_range+0x20/0x20
> 	cpuhp_thread_fun+0xb0/0x110
> 	smpboot_thread_fn+0xef/0x160
> 	kthread+0x113/0x130
> 	kthread_create_worker_on_cpu+0x70/0x70
> 	ret_from_fork+0x35/0x40
> 
> To avoid this issue, don't forcibly set the CPB capability for a CPU
> when running under a hypervisor.
> 
> Signed-off-by: Frank van der Linden <fllinden@amazon.com>
> Fixes: 0237199186e7 ("x86/CPU/AMD: Set the CPB bit unconditionally on F17h")
> ---
>  arch/x86/kernel/cpu/amd.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index fb6a64bd765f..ee4d79fa1b19 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -823,8 +823,11 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
>  {
>  	set_cpu_cap(c, X86_FEATURE_ZEN);
>  
> -	/* Fix erratum 1076: CPB feature bit not being set in CPUID. */
> -	if (!cpu_has(c, X86_FEATURE_CPB))
> +	/*
> +	 * Fix erratum 1076: CPB feature bit not being set in CPUID.
> +	 * Always set it, except when running under a hypervisor.
> +	 */
> +	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
>  		set_cpu_cap(c, X86_FEATURE_CPB);
>  }

I guess...

Acked-by: Borislav Petkov <bp@suse.de>

Btw, it has come up before whether it would be additionally prudent
to replace those *msr calls with their *msr_safe counterparts, in
boost_set_msr() and also check *msr_safe() retvals and exit early there.
Just in case and exactly because of virt.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply. Srsly.

[tip:x86/urgent] x86/CPU/AMD: Don't force the CPB cap when running under a hypervisor

[tip-bot for Frank van der Linden]

Commit-ID:  2ac44ab608705948564791ce1d15d43ba81a1e38
Gitweb:     https://git.kernel.org/tip/2ac44ab608705948564791ce1d15d43ba81a1e38
Author:     Frank van der Linden <fllinden@amazon.com>
AuthorDate: Wed, 22 May 2019 22:17:45 +0000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 24 May 2019 08:50:32 +0200

x86/CPU/AMD: Don't force the CPB cap when running under a hypervisor

For F17h AMD CPUs, the CPB capability ('Core Performance Boost') is forcibly set,
because some versions of that chip incorrectly report that they do not have it.

However, a hypervisor may filter out the CPB capability, for good
reasons. For example, KVM currently does not emulate setting the CPB
bit in MSR_K7_HWCR, and unchecked MSR access errors will be thrown
when trying to set it as a guest:

	unchecked MSR access error: WRMSR to 0xc0010015 (tried to write 0x0000000001000011) at rIP: 0xffffffff890638f4 (native_write_msr+0x4/0x20)

	Call Trace:
	boost_set_msr+0x50/0x80 [acpi_cpufreq]
	cpuhp_invoke_callback+0x86/0x560
	sort_range+0x20/0x20
	cpuhp_thread_fun+0xb0/0x110
	smpboot_thread_fn+0xef/0x160
	kthread+0x113/0x130
	kthread_create_worker_on_cpu+0x70/0x70
	ret_from_fork+0x35/0x40

To avoid this issue, don't forcibly set the CPB capability for a CPU
when running under a hypervisor.

Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Acked-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bp@alien8.de
Cc: jiaxun.yang@flygoat.com
Fixes: 0237199186e7 ("x86/CPU/AMD: Set the CPB bit unconditionally on F17h")
Link: http://lkml.kernel.org/r/20190522221745.GA15789@dev-dsk-fllinden-2c-c1893d73.us-west-2.amazon.com
[ Minor edits to the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/cpu/amd.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 80a405c2048a..8d4e50428b68 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -824,8 +824,11 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
 {
 	set_cpu_cap(c, X86_FEATURE_ZEN);
 
-	/* Fix erratum 1076: CPB feature bit not being set in CPUID. */
-	if (!cpu_has(c, X86_FEATURE_CPB))
+	/*
+	 * Fix erratum 1076: CPB feature bit not being set in CPUID.
+	 * Always set it, except when running under a hypervisor.
+	 */
+	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
 		set_cpu_cap(c, X86_FEATURE_CPB);
 }