linux-kernel - Re: [PATCH v13 05/13] x86/sev: Prevent RDTSC/RDTSCP interception for Secure TSC enabled guests

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Message-ID: <aff9bf82-e11e-43d9-8661-aefa328242ad@intel.com>
Date: Thu, 24 Oct 2024 15:56:35 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org,
 thomas.lendacky@....com, 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 05/13] x86/sev: Prevent RDTSC/RDTSCP interception for
 Secure TSC enabled guests

On 10/21/2024 1:51 PM, Nikunj A Dadhania wrote:
> The hypervisor should not be intercepting RDTSC/RDTSCP when Secure TSC is
> enabled. A #VC exception will be generated if the RDTSC/RDTSCP instructions
> are being intercepted. If this should occur and Secure TSC is enabled,
> terminate guest execution.

There is another option to ignore the interception and just return back 
to guest execution. I think it better to add some justification on why 
make it fatal and terminate the guest is better than ignoring the 
interception.

> Signed-off-by: Nikunj A Dadhania <nikunj@....com>
> Tested-by: Peter Gonda <pgonda@...gle.com>
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>   arch/x86/coco/sev/shared.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/arch/x86/coco/sev/shared.c b/arch/x86/coco/sev/shared.c
> index 71de53194089..c2a9e2ada659 100644
> --- a/arch/x86/coco/sev/shared.c
> +++ b/arch/x86/coco/sev/shared.c
> @@ -1140,6 +1140,16 @@ static enum es_result vc_handle_rdtsc(struct ghcb *ghcb,
>   	bool rdtscp = (exit_code == SVM_EXIT_RDTSCP);
>   	enum es_result ret;
>   
> +	/*
> +	 * RDTSC and RDTSCP should not be intercepted when Secure TSC is
> +	 * enabled. Terminate the SNP guest when the interception is enabled.
> +	 * This file is included from kernel/sev.c and boot/compressed/sev.c,
> +	 * use sev_status here as cc_platform_has() is not available when
> +	 * compiling boot/compressed/sev.c.
> +	 */
> +	if (sev_status & MSR_AMD64_SNP_SECURE_TSC)
> +		return ES_VMM_ERROR;
> +
>   	ret = sev_es_ghcb_hv_call(ghcb, ctxt, exit_code, 0, 0);
>   	if (ret != ES_OK)
>   		return ret;