linux-kernel - Re: [PATCH v7 10/16] x86/sev: Add Secure TSC support for SNP guests

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Message-ID: <CABgObfYwtMQY-E+ENs3z8Ew-Yc7tiXC7PmdvFjPcUeXqOMY8PQ@mail.gmail.com>
Date: Thu, 1 Feb 2024 16:46:12 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Nikunj A Dadhania <nikunj@....com>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, x86@...nel.org, 
	kvm@...r.kernel.org, bp@...en8.de, mingo@...hat.com, tglx@...utronix.de, 
	dave.hansen@...ux.intel.com, dionnaglaze@...gle.com, pgonda@...gle.com, 
	seanjc@...gle.com
Subject: Re: [PATCH v7 10/16] x86/sev: Add Secure TSC support for SNP guests

On Wed, Dec 20, 2023 at 4:16 PM Nikunj A Dadhania <nikunj@....com> wrote:

> +       /* Setting Secure TSC parameters */
> +       if (cpu_feature_enabled(X86_FEATURE_SNP_SECURE_TSC)) {
> +               vmsa->tsc_scale = snp_tsc_scale;
> +               vmsa->tsc_offset = snp_tsc_offset;
> +       }

This needs to use guest_cpu_has, otherwise updating the hypervisor or
processor will change the initial VMSA and any measurement derived
from there.

In fact, the same issue exists for DEBUG_SWAP and I will shortly post
a series to allow enabling/disabling DEBUG_SWAP per-VM, so that
updating the kernel does not break existing measurements.

Paolo