linux-kernel - Re: [PATCH 1/3] KVM: x86, vmx: Add function for event delivery error generation

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Message-ID: <ZxAqscbrROD1_szG@google.com>
Date: Wed, 16 Oct 2024 14:05:53 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Ivan Orlov <iorlov@...zon.com>
Cc: bp@...en8.de, dave.hansen@...ux.intel.com, mingo@...hat.com, 
	pbonzini@...hat.com, shuah@...nel.org, tglx@...utronix.de, hpa@...or.com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, x86@...nel.org, jalliste@...zon.com, 
	nh-open-source@...zon.com, pdurrant@...zon.co.uk
Subject: Re: [PATCH 1/3] KVM: x86, vmx: Add function for event delivery error generation

On Tue, Oct 15, 2024, Ivan Orlov wrote:
> > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > > index c67e448c6ebd..afd785e7f3a3 100644
> > > --- a/arch/x86/kvm/vmx/vmx.c
> > > +++ b/arch/x86/kvm/vmx/vmx.c
> > > @@ -6550,19 +6550,10 @@ static int __vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
> > >  	     exit_reason.basic != EXIT_REASON_APIC_ACCESS &&
> > >  	     exit_reason.basic != EXIT_REASON_TASK_SWITCH &&
> > >  	     exit_reason.basic != EXIT_REASON_NOTIFY)) {
> > > -		int ndata = 3;
> > > +		gpa_t gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
> > > +		bool is_mmio = exit_reason.basic == EXIT_REASON_EPT_MISCONFIG;
> > 
> > There's no need for is_mmio, just pass INVALID_GPA when the GPA isn't known.
> 
> Ah alright, then we definitely don't need an is_mmio field. I assume we
> can't do MMIO at GPA=0, right?

Wrong :-)

>From an architectural perspective, GPA=0 is not special in any way.  E.g. prior
to L1TF, Linux would happily use the page with PFN=0.