Re: [PATCH v3 2/8] x86/sev: Add support for the RMPREAD instruction

[Nikunj A. Dadhania]

On 9/30/2024 8:52 PM, Tom Lendacky wrote:
> The RMPREAD instruction returns an architecture defined format of an
> RMP table entry. This is the preferred method for examining RMP entries.
> 
> The instruction is advertised in CPUID 0x8000001f_EAX[21]. Use this
> instruction when available.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

Reviewed-by: Nikunj A Dadhania <nikunj@xxxxxxx>

> ---
>  arch/x86/include/asm/cpufeatures.h |  1 +
>  arch/x86/virt/svm/sev.c            | 11 +++++++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index dd4682857c12..93620a4c5b15 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -447,6 +447,7 @@
>  #define X86_FEATURE_V_TSC_AUX		(19*32+ 9) /* Virtual TSC_AUX */
>  #define X86_FEATURE_SME_COHERENT	(19*32+10) /* AMD hardware-enforced cache coherency */
>  #define X86_FEATURE_DEBUG_SWAP		(19*32+14) /* "debug_swap" AMD SEV-ES full debug state swap support */
> +#define X86_FEATURE_RMPREAD		(19*32+21) /* RMPREAD instruction */
>  #define X86_FEATURE_SVSM		(19*32+28) /* "svsm" SVSM present */
>  
>  /* AMD-defined Extended Feature 2 EAX, CPUID level 0x80000021 (EAX), word 20 */
> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> index 103a2dd6e81d..73d4f422829a 100644
> --- a/arch/x86/virt/svm/sev.c
> +++ b/arch/x86/virt/svm/sev.c
> @@ -301,6 +301,17 @@ static int get_rmpentry(u64 pfn, struct rmpentry *entry)
>  {
>  	struct rmpentry_raw *e;
>  
> +	if (cpu_feature_enabled(X86_FEATURE_RMPREAD)) {
> +		int ret;
> +
> +		asm volatile(".byte 0xf2, 0x0f, 0x01, 0xfd"
> +			     : "=a" (ret)
> +			     : "a" (pfn << PAGE_SHIFT), "c" (entry)
> +			     : "memory", "cc");
> +
> +		return ret;
> +	}
> +
>  	e = __get_rmpentry(pfn);
>  	if (IS_ERR(e))
>  		return PTR_ERR(e);