linux-kernel - Re: [PATCH 3/5] KVM: x86/xen: Consult kvm_xen_enabled when checking for Xen MSR writes

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Message-ID: <2f4752d5-63ec-4e7f-bb7a-a97eecfdfb18@xen.org>
Date: Mon, 3 Feb 2025 09:15:06 +0000
From: Paul Durrant <xadimgnik@...il.com>
To: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, David Woodhouse <dwmw2@...radead.org>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 syzbot+cdeaeec70992eca2d920@...kaller.appspotmail.com,
 Joao Martins <joao.m.martins@...cle.com>, David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [PATCH 3/5] KVM: x86/xen: Consult kvm_xen_enabled when checking
 for Xen MSR writes

On 01/02/2025 01:13, Sean Christopherson wrote:
> Query kvm_xen_enabled when detecting writes to the Xen hypercall page MSR
> so that the check is optimized away in the likely scenario that Xen isn't
> enabled for the VM.
> 
> Deliberately open code the check instead of using kvm_xen_msr_enabled() in
> order to avoid a double load of xen_hvm_config.msr (which is admittedly
> rather pointless given the widespread lack of READ_ONCE() usage on the
> plethora of vCPU-scoped accesses to kvm->arch.xen state).
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/xen.h | 3 +++
>   1 file changed, 3 insertions(+)
> 

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