linux-kernel - Re: [PATCH v13 06/13] x86/sev: Prevent GUEST_TSC_FREQ MSR interception for Secure TSC enabled guests

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Message-ID: <85964a1e-61e5-c75c-c670-c41f640a8e7a@amd.com>
Date: Tue, 22 Oct 2024 09:50:18 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Tom Lendacky <thomas.lendacky@....com>, linux-kernel@...r.kernel.org,
 bp@...en8.de, x86@...nel.org, kvm@...r.kernel.org
Cc: mingo@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com,
 pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v13 06/13] x86/sev: Prevent GUEST_TSC_FREQ MSR
 interception for Secure TSC enabled guests

On 10/21/2024 7:38 PM, Tom Lendacky wrote:
> On 10/21/24 00:51, Nikunj A Dadhania wrote:
>> The hypervisor should not be intercepting GUEST_TSC_FREQ MSR(0xcOO10134)
>> when Secure TSC is enabled. A #VC exception will be generated if the
>> GUEST_TSC_FREQ MSR is being intercepted. If this should occur and SecureTSC
>> is enabled, terminate guest execution.
>>
>> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> 
> Just a minor comment/question below.
> 
..
>> diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
>> index 2ad7773458c0..4e9b1cc1f26b 100644
>> --- a/arch/x86/coco/sev/core.c
>> +++ b/arch/x86/coco/sev/core.c
>> @@ -1332,6 +1332,14 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
>>  		return ES_OK;
>>  	}
>>  
>> +	/*
>> +	 * GUEST_TSC_FREQ should not be intercepted when Secure TSC is
>> +	 * enabled. Terminate the SNP guest when the interception is enabled.
>> +	 */
>> +	if (regs->cx == MSR_AMD64_GUEST_TSC_FREQ && cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
> 
> Should the cc_platform_has() check be changed into a check against
> sev_status directly (similar to the DEBUG_SWAP support)? Just in case
> this handler ends up getting used in early code where cc_platform_has()
> can't be used.

Sure, that makes sense. I will change it in my next version.

Regards
Nikunj