linux-kernel - Re: [PATCH v15 06/13] x86/sev: Prevent GUEST_TSC_FREQ MSR interception for Secure TSC enabled guests

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Message-ID: <fe09ff1d-4a9b-4307-92c0-767cd3974152@amd.com>
Date: Thu, 2 Jan 2025 15:00:07 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: thomas.lendacky@....com, linux-kernel@...r.kernel.org, x86@...nel.org,
 kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
 dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com,
 pbonzini@...hat.com
Subject: Re: [PATCH v15 06/13] x86/sev: Prevent GUEST_TSC_FREQ MSR
 interception for Secure TSC enabled guests

On 1/2/2025 2:37 PM, Borislav Petkov wrote:
> On Thu, Jan 02, 2025 at 10:33:26AM +0530, Nikunj A. Dadhania wrote:

> As in: I will handle the TSC MSRs for STSC guests and the other flow for
> non-STSC guests should remain. For now.
> 
> And make that goddamn explicit.
> 
> One possible way to do that is this:

I agree, if renaming helps to make it explicit, this is perfect. Thanks.

> 
> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
> index 6235286a0eda..61100532c259 100644
> --- a/arch/x86/coco/sev/core.c
> +++ b/arch/x86/coco/sev/core.c
> @@ -1439,7 +1439,7 @@ static enum es_result __vc_handle_msr_caa(struct pt_regs *regs, bool write)
>   * Reads:  Reads of MSR_IA32_TSC should return the current TSC
>   *         value, use the value returned by RDTSC.
>   */
> -static enum es_result __vc_handle_msr_tsc(struct pt_regs *regs, bool write)
> +static enum es_result __vc_handle_secure_tsc_msrs(struct pt_regs *regs, bool write)
>  {
>  	u64 tsc;
>  
> @@ -1477,7 +1477,9 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
>  	case MSR_IA32_TSC:
>  	case MSR_AMD64_GUEST_TSC_FREQ:
>  		if (sev_status & MSR_AMD64_SNP_SECURE_TSC)
> -			return __vc_handle_msr_tsc(regs, write);
> +			return __vc_handle_secure_tsc_msrs(regs, write);
> +		else
> +			break;
>  	default:
>  		break;
>  	}
> ---

Regards,
Nikunj