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: <2419362fac13e7e87044df1ec8b2eb782135c5c8.camel@infradead.org>
Date: Thu, 06 Feb 2025 16:29:42 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>,  Paul Durrant <paul@....org>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzbot+cdeaeec70992eca2d920@...kaller.appspotmail.com, Joao Martins
	 <joao.m.martins@...cle.com>
Subject: Re: [PATCH 3/5] KVM: x86/xen: Consult kvm_xen_enabled when checking
 for Xen MSR writes

On Fri, 2025-01-31 at 17:13 -0800, 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>

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


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