linux-kernel - Re: [PATCH 1/5] KVM: x86: Re-enter guest if WRMSR(X2APIC

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Message-ID: <ZtdATR4DY1A9K5ad@google.com>
Date: Tue, 3 Sep 2024 09:58:53 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] KVM: x86: Re-enter guest if WRMSR(X2APIC_ICR)
 fastpath is successful

On Tue, Sep 03, 2024, Paolo Bonzini wrote:
> On Tue, Sep 3, 2024 at 5:09 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > On Mon, Sep 02, 2024, Paolo Bonzini wrote:
> > > On Fri, Aug 2, 2024 at 9:51 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > > > Re-enter the guest in the fastpath if WRMSR emulation for x2APIC's ICR is
> > > > successful, as no additional work is needed, i.e. there is no code unique
> > > > for WRMSR exits between the fastpath and the "!= EXIT_FASTPATH_NONE" check
> > > > in __vmx_handle_exit().
> > >
> > > What about if you send an IPI to yourself?  Doesn't that return true
> > > for kvm_vcpu_exit_request() if posted interrupts are disabled?
> >
> > Yes, but that doesn't have anything to do with WRMSR itself, as KVM needs to morph
> > EXIT_FASTPATH_EXIT_HANDLED => EXIT_FASTPATH_REENTER_GUEST if there's a pending
> > event that needs requires injection.
> 
> The other way round? i.e. treat EXIT_FASTPATH_REENTER_GUEST as
> EXIT_FASTPATH_EXIT_HANDLED to go through event injection.

Doh, yes.