linux-kernel - Re: [PATCH v3 3/8] x86/sev: Require the RMPREAD instruction after Fam19h

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Message-ID: <de96cad3-6591-4084-b02a-e0b2c27c525b@amd.com>
Date: Fri, 18 Oct 2024 09:56:25 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: Tom Lendacky <thomas.lendacky@....com>, linux-kernel@...r.kernel.org,
 x86@...nel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Michael Roth <michael.roth@....com>, Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH v3 3/8] x86/sev: Require the RMPREAD instruction after
 Fam19h



On 9/30/2024 8:52 PM, Tom Lendacky wrote:
> Limit usage of the non-architectural RMP format to Fam19h processors.
> The RMPREAD instruction, with its architecture defined output, is
> available, and should be used, for RMP access beyond Fam19h.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/kernel/cpu/amd.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 015971adadfc..ddbb6dd75fb2 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -358,7 +358,8 @@ static void bsp_determine_snp(struct cpuinfo_x86 *c)
>  		 * for which the RMP table entry format is currently defined for.
>  		 */
>  		if (!cpu_has(c, X86_FEATURE_HYPERVISOR) &&
> -		    c->x86 >= 0x19 && snp_probe_rmptable_info()) {
> +		    (c->x86 == 0x19 || cpu_feature_enabled(X86_FEATURE_RMPREAD)) &&

Maybe update the comment above this if condition with information about RMPREAD FEAT?


- Neeraj

> +		    snp_probe_rmptable_info()) {
>  			cc_platform_set(CC_ATTR_HOST_SEV_SNP);
>  		} else {
>  			setup_clear_cpu_cap(X86_FEATURE_SEV_SNP);