[PATCH v3 2/3] KVM: x86: Drop superfluous caching of KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT

[Sean Christopherson <seanjc@google.com>]

Drop kvm_vcpu_arch.delivery_as_pf_vmexit and instead use msr_en_val as the
source of truth to reduce the probability of operating on stale data.  This
fixes flaws where KVM fails to update delivery_as_pf_vmexit when APF is
explicitly disabled by the guest or implicitly disabled by KVM on INIT.
Absent other bugs, the flaws are benign as KVM *shouldn't* consume
delivery_as_pf_vmexit when PV APF support is disabled.

Simply delete the field, as there's zero benefit to maintaining a separate
"cache" of the state.

Fixes: 52a5c155cf79 ("KVM: async_pf: Let guest support delivery of async_pf from guest mode")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/include/asm/kvm_host.h | 1 -
 arch/x86/kvm/x86.c              | 3 +--
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index c470e40a00aa..fae1f4aeca5a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1039,7 +1039,6 @@ struct kvm_vcpu_arch {
 		u32 id;
 		u32 host_apf_flags;
 		bool send_always;
-		bool delivery_as_pf_vmexit;
 		bool pageready_pending;
 	} apf;
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c35d359b56dd..4632222a5d1c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3666,7 +3666,6 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
 	}
 
 	vcpu->arch.apf.send_always = (data & KVM_ASYNC_PF_SEND_ALWAYS);
-	vcpu->arch.apf.delivery_as_pf_vmexit = data & KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT;
 
 	kvm_async_pf_wakeup_all(vcpu);
 
@@ -14035,7 +14034,7 @@ static bool kvm_can_deliver_async_pf(struct kvm_vcpu *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;
+		return vcpu->arch.apf.msr_en_val & KVM_ASYNC_PF_DELIVERY_AS_PF_VMEXIT;
 	} else {
 		/*
 		 * Play it safe in case the guest temporarily disables paging.
-- 
2.53.0.1213.gd9a14994de-goog