[PATCH] x86/cpufeatures: Define X86_FEATURE_PREFETCHI (AMD)

[PATCH] x86/cpufeatures: Define X86_FEATURE_PREFETCHI (AMD)

[Babu Moger]

The latest AMD platform has introduced a new instruction called PREFETCHI.
This instruction loads a cache line from a specified memory address into
the indicated data or instruction cache level, based on locality reference
hints.

Feature bit definition:
CPUID_Fn80000021_EAX [bit 20] - Indicates support for IC prefetch.

This feature is analogous to Intel's PREFETCHITI (CPUID.(EAX=7,ECX=1):EDX),
though the CPUID bit definitions differ between AMD and Intel.

Expose the feature to KVM guests.

The feature is documented in Processor Programming Reference (PPR)
for AMD Family 1Ah Model 02h, Revision C1 (Link below).

Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
Signed-off-by: Babu Moger <babu.moger@amd.com>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kvm/cpuid.c               | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 6c2c152d8a67..7d7507b3eefd 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -457,6 +457,7 @@
 #define X86_FEATURE_AUTOIBRS		(20*32+ 8) /* Automatic IBRS */
 #define X86_FEATURE_NO_SMM_CTL_MSR	(20*32+ 9) /* SMM_CTL MSR is not present */
 
+#define X86_FEATURE_PREFETCHI		(20*32+20) /* Prefetch Data/Instruction to Cache Level */
 #define X86_FEATURE_SBPB		(20*32+27) /* Selective Branch Prediction Barrier */
 #define X86_FEATURE_IBPB_BRTYPE		(20*32+28) /* MSR_PRED_CMD[IBPB] flushes all branch type predictions */
 #define X86_FEATURE_SRSO_NO		(20*32+29) /* CPU is not affected by SRSO */
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 5e4d4934c0d3..fba018a730ab 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1178,6 +1178,7 @@ void kvm_set_cpu_caps(void)
 		/* SmmPgCfgLock */
 		F(NULL_SEL_CLR_BASE),
 		F(AUTOIBRS),
+		F(PREFETCHI),
 		EMULATED_F(NO_SMM_CTL_MSR),
 		/* PrefetchCtlMsr */
 		F(WRMSR_XX_BASE_NS),
-- 
2.34.1

Re: [PATCH] x86/cpufeatures: Define X86_FEATURE_PREFETCHI (AMD)

[Borislav Petkov]

On Tue, Apr 08, 2025 at 05:57:09PM -0500, Babu Moger wrote:
> The latest AMD platform has introduced a new instruction called PREFETCHI.
> This instruction loads a cache line from a specified memory address into
> the indicated data or instruction cache level, based on locality reference
> hints.
> 
> Feature bit definition:
> CPUID_Fn80000021_EAX [bit 20] - Indicates support for IC prefetch.
> 
> This feature is analogous to Intel's PREFETCHITI (CPUID.(EAX=7,ECX=1):EDX),
> though the CPUID bit definitions differ between AMD and Intel.
> 
> Expose the feature to KVM guests.
> 
> The feature is documented in Processor Programming Reference (PPR)
> for AMD Family 1Ah Model 02h, Revision C1 (Link below).
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  arch/x86/kvm/cpuid.c               | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 6c2c152d8a67..7d7507b3eefd 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -457,6 +457,7 @@
>  #define X86_FEATURE_AUTOIBRS		(20*32+ 8) /* Automatic IBRS */
>  #define X86_FEATURE_NO_SMM_CTL_MSR	(20*32+ 9) /* SMM_CTL MSR is not present */
>  
> +#define X86_FEATURE_PREFETCHI		(20*32+20) /* Prefetch Data/Instruction to Cache Level */
>  #define X86_FEATURE_SBPB		(20*32+27) /* Selective Branch Prediction Barrier */
>  #define X86_FEATURE_IBPB_BRTYPE		(20*32+28) /* MSR_PRED_CMD[IBPB] flushes all branch type predictions */
>  #define X86_FEATURE_SRSO_NO		(20*32+29) /* CPU is not affected by SRSO */

Acked-by: Borislav Petkov (AMD) <bp@alien8.de>

-- 
Regards/Gruss,
    Boris.

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

Re: [PATCH] x86/cpufeatures: Define X86_FEATURE_PREFETCHI (AMD)

[Sean Christopherson]

On Tue, 08 Apr 2025 17:57:09 -0500, Babu Moger wrote:
> The latest AMD platform has introduced a new instruction called PREFETCHI.
> This instruction loads a cache line from a specified memory address into
> the indicated data or instruction cache level, based on locality reference
> hints.
> 
> Feature bit definition:
> CPUID_Fn80000021_EAX [bit 20] - Indicates support for IC prefetch.
> 
> [...]

Applied to kvm-x86 misc, with a rewritten shortlog and changelog to make it super
clear this is KVM enabling.

[1/1] KVM: x86: Advertise support for AMD's PREFETCHI
      https://github.com/kvm-x86/linux/commit/d88bb2ded2ef

--
https://github.com/kvm-x86/linux/tree/next

Re: [PATCH] x86/cpufeatures: Define X86_FEATURE_PREFETCHI (AMD)

[Moger, Babu]

On 4/25/25 18:23, Sean Christopherson wrote:
> On Tue, 08 Apr 2025 17:57:09 -0500, Babu Moger wrote:
>> The latest AMD platform has introduced a new instruction called PREFETCHI.
>> This instruction loads a cache line from a specified memory address into
>> the indicated data or instruction cache level, based on locality reference
>> hints.
>>
>> Feature bit definition:
>> CPUID_Fn80000021_EAX [bit 20] - Indicates support for IC prefetch.
>>
>> [...]
> 
> Applied to kvm-x86 misc, with a rewritten shortlog and changelog to make it super
> clear this is KVM enabling.

Sean, Thank you.
Babu Moger