linux-kernel - Re: [PATCH 5/6] KVM: VMX: Always intercept accesses to unsupported "extended" x2APIC regs

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Date:   Mon, 9 Jan 2023 09:25:09 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Marc Orr <marcorr@...gle.com>,
        Ben Gardon <bgardon@...gle.com>,
        Venkatesh Srinivas <venkateshs@...omium.org>
Subject: Re: [PATCH 5/6] KVM: VMX: Always intercept accesses to unsupported
 "extended" x2APIC regs

On Fri, Jan 6, 2023 at 5:10 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> Don't clear the "read" bits for x2APIC registers above SELF_IPI (APIC regs

Odd use of quotation marks in the shortlog  and here.

> 0x400 - 0xff0, MSRs 0x840 - 0x8ff).  KVM doesn't emulate registers in that
> space (there are a smattering of AMD-only extensions) and so should
> intercept reads in order to inject #GP.  When APICv is fully enabled,
> Intel hardware doesn't validate the registers on RDMSR and instead blindly
> retrieves data from the vAPIC page, i.e. it's software's responsibility to
> intercept reads to non-existent MSRs.
>
> Fixes: 8d14695f9542 ("x86, apicv: add virtual x2apic support")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>