linux-kernel - Re: [PATCH 03/12] KVM: x86: do not deliver asynchronous page faults if CR0.PG=0

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Date:   Fri, 11 Feb 2022 12:16:29 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        vkuznets@...hat.com, mlevitsk@...hat.com, dmatlack@...gle.com
Subject: Re: [PATCH 03/12] KVM: x86: do not deliver asynchronous page faults
 if CR0.PG=0

On 2/11/22 00:16, Sean Christopherson wrote:
> Third time's a charm...
> 
> 	if (kvm_pv_async_pf_enabled(vcpu))
> 		return false;
> 
> 	if (vcpu->arch.apf.send_user_only &&
> 	    static_call(kvm_x86_get_cpl)(vcpu) == 0)
> 		return false;
> 
> 	/* L1 CR0.PG=1 is guaranteed if the vCPU is in guest mode (L2). */
> 	if (is_guest_mode(vcpu))
> 		return !vcpu->arch.apf.delivery_as_pf_vmexit;
> 
> 	return is_paging(vcpu);
> 
> 

Went for this, but with slightly different final "if":

         if (is_guest_mode(vcpu)) {
                 /*
                  * L1 needs to opt into the special #PF vmexits that are
                  * used to deliver async page faults.
                  */
                 return vcpu->arch.apf.delivery_as_pf_vmexit;
         } else {
                 /*
                  * Play it safe in case the guest does a quick real mode
                  * foray.  The real mode IDT is unlikely to have a #PF
                  * exception setup.
                  */
                 return is_paging(vcpu);
         }

Paolo