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

[Sean Christopherson <seanjc@google.com>]

Drop kvm_vcpu_arch.send_always 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 send_always 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 send_always when PV
APF support is disabled.

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

Opportunistically turn the enabled vs. disabled logic at the end of
kvm_pv_enable_async_pf() into an if-else instead of using an early return,
e.g. so that it's more obvious that both paths are "success" paths.

Fixes: 6adba5274206 ("KVM: Let host know whether the guest can handle async PF in non-userspace context.")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/include/asm/kvm_host.h |  1 -
 arch/x86/kvm/x86.c              | 12 ++++--------
 2 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index fae1f4aeca5a..2a6906597637 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1038,7 +1038,6 @@ struct kvm_vcpu_arch {
 		u16 vec;
 		u32 id;
 		u32 host_apf_flags;
-		bool send_always;
 		bool pageready_pending;
 	} apf;
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4632222a5d1c..e24877353f17 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3659,16 +3659,12 @@ static int kvm_pv_enable_async_pf(struct kvm_vcpu *vcpu, u64 data)
 
 	vcpu->arch.apf.msr_en_val = data;
 
-	if (!__kvm_pv_async_pf_enabled(data)) {
+	if (__kvm_pv_async_pf_enabled(data)) {
+		kvm_async_pf_wakeup_all(vcpu);
+	} else {
 		kvm_clear_async_pf_completion_queue(vcpu);
 		kvm_async_pf_hash_reset(vcpu);
-		return 0;
 	}
-
-	vcpu->arch.apf.send_always = (data & KVM_ASYNC_PF_SEND_ALWAYS);
-
-	kvm_async_pf_wakeup_all(vcpu);
-
 	return 0;
 }
 
@@ -14025,7 +14021,7 @@ static bool kvm_can_deliver_async_pf(struct kvm_vcpu *vcpu)
 	if (!kvm_pv_async_pf_enabled(vcpu))
 		return false;
 
-	if (!vcpu->arch.apf.send_always &&
+	if (!(vcpu->arch.apf.msr_en_val & KVM_ASYNC_PF_SEND_ALWAYS) &&
 	    (vcpu->arch.guest_state_protected || !kvm_x86_call(get_cpl)(vcpu)))
 		return false;
 
-- 
2.53.0.1213.gd9a14994de-goog