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

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Message-ID: <c1399dbe-3987-4236-9b21-fe54e99651d5@gmail.com>
Date: Sun, 26 Jan 2025 16:15:50 +0000
From: "Durrant, Paul" <xadimgnik@...il.com>
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>, David Woodhouse <dwmw2@...radead.org>,
 Paul Durrant <paul@....org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Update Xen TSC leaves during CPUID emulation

On 24/01/2025 15:05, 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>
> ---
>   arch/x86/kvm/cpuid.c | 16 ++++++++++++++++
>   arch/x86/kvm/x86.c   |  3 +--
>   arch/x86/kvm/x86.h   |  1 +
>   arch/x86/kvm/xen.c   | 23 -----------------------
>   arch/x86/kvm/xen.h   | 13 +++++++++++--
>   5 files changed, 29 insertions(+), 27 deletions(-)
> 

Reviewed-by: Paul Durrant <paul@....org>