[PATCH 3/3] KVM: x86: never write to memory from kvm_vcpu_check_block

From: Paolo Bonzini <pbonzini@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: mlevitsk@redhat.com, seanjc@google.com, stable@vger.kernel.org
Subject: [PATCH 3/3] KVM: x86: never write to memory from kvm_vcpu_check_block
Date: Wed, 27 Apr 2022 13:37:58 -0400	[thread overview]
Message-ID: <20220427173758.517087-4-pbonzini@redhat.com> (raw)
In-Reply-To: <20220427173758.517087-1-pbonzini@redhat.com>

kvm_vcpu_check_block is called while not in TASK_RUNNING, and therefore
cannot sleep.  Writing to guest memory is therefore forbidden, but it
can happen if kvm_check_nested_events causes a vmexit.

Fortunately, all events that are caught by kvm_check_nested_events are
also handled by kvm_vcpu_has_events through vendor callbacks such as
kvm_x86_interrupt_allowed or kvm_x86_ops.nested_ops->has_events, so
remove the call.

Cc: stable@vger.kernel.org
Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/x86.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d563812ca229..90b4f50b9a84 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10341,9 +10341,6 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu)
 
 static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
 {
-	if (is_guest_mode(vcpu))
-		kvm_check_nested_events(vcpu);
-
 	return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
 		!vcpu->arch.apf.halted);
 }
-- 
2.31.1

