linux-kernel - Re: [PATCH v2] KVM: x86: Update Xen TSC leaves during CPUID emulation

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Message-ID: <393b23182f50653b8270d26c41e1f7a010e5d7d6.camel@infradead.org>
Date: Tue, 28 Jan 2025 10:34:32 -0800
From: David Woodhouse <dwmw2@...radead.org>
To: Fred Griffoul <fgriffo@...zon.co.uk>, kvm@...r.kernel.org
Cc: griffoul@...il.com, vkuznets@...hat.com, Sean Christopherson
 <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner
 <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
 <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Paul Durrant <paul@....org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Update Xen TSC leaves during CPUID
 emulation

On Fri, 2025-01-24 at 15:05 +0000, Fred Griffoul wrote:
> The Xen emulation in KVM modifies certain CPUID leaves to expose
> TSC information to the guest.
> 
> Previously, these CPUID leaves were updated whenever guest time changed,
> but this conflicts with KVM_SET_CPUID/KVM_SET_CPUID2 ioctls which reject
> changes to CPUID entries on running vCPUs.
> 
> Fix this by updating the TSC information directly in the CPUID emulation
> handler instead of modifying the vCPU's CPUID entries.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Fred Griffoul <fgriffo@...zon.co.uk>

Reviewed-by: David Woodhouse <dwmw@...zon.co.uk>

But I would still like to see a selftest covering it.

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