From: Sean Christopherson <seanjc@google.com>
To: Naveen N Rao <naveen@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] KVM: SVM: Only disable x2AVIC WRMSR interception for MSRs that are accelerated
Date: Fri, 10 Apr 2026 10:19:37 -0700 [thread overview]
Message-ID: <adkxKVIFnOyG3umd@google.com> (raw)
In-Reply-To: <adkqDG_2UouUjDFD@blrnaveerao1>
On Fri, Apr 10, 2026, Naveen N Rao wrote:
> On Thu, Apr 09, 2026 at 03:24:49PM -0700, Sean Christopherson wrote:
> > When x2AVIC is enabled, disable WRMSR interception only for MSRs that are
> > actually accelerated by hardware. Disabling interception for MSRs that
> > aren't accelerated is functionally "fine", but very suboptimal as many
> > accesses generate AVIC_UNACCELERATED_ACCESS fault #VMEXITs, which requires
> > KVM to decode the instruction to figure out what the guest was trying to
> > access.
>
> Not sure I follow: as far as I can see, most writes are actually trapped
> except for MSRs that are supposed to be RO?
Yeah, that's what I was trying to say by "only for MSRs that are actually
accelerated by hardware". Oh, but that's bad verbiage, because trap-like
#VMEXITs are also due to lack of acceleration, it's specifically "software is
being stupid" that triggers fault-like exits.
prev parent reply other threads:[~2026-04-10 17:19 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-09 22:24 [PATCH 0/3] KVM: SVM: Fix x2AVIC MSR interception mess Sean Christopherson
2026-04-09 22:24 ` [PATCH 1/3] KVM: SVM: Disable x2AVIC RDMSR interception for MSRs KVM actually supports Sean Christopherson
2026-04-10 16:45 ` Naveen N Rao
2026-04-10 19:20 ` Sean Christopherson
2026-04-09 22:24 ` [PATCH 2/3] KVM: SVM: Always intercept RDMSR for TMCCT (current APIC timer count) Sean Christopherson
2026-04-09 22:24 ` [PATCH 3/3] KVM: SVM: Only disable x2AVIC WRMSR interception for MSRs that are accelerated Sean Christopherson
2026-04-10 16:53 ` Naveen N Rao
2026-04-10 17:19 ` Sean Christopherson [this message]
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