linux-kernel - [PATCH] KVM: VMX: Remove redundant handling of bus lock vmexit

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Message-Id: <1632722002-25003-1-git-send-email-hao.xiang@linux.alibaba.com>
Date:   Mon, 27 Sep 2021 13:53:22 +0800
From:   Hao Xiang <hao.xiang@...ux.alibaba.com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        seanjc@...gle.com, shannon.zhao@...ux.alibaba.com,
        Hao Xiang <hao.xiang@...ux.alibaba.com>
Subject: [PATCH] KVM: VMX: Remove redundant handling of bus lock vmexit

exit_reason.bus_lock_detected may or may not be set when exit reason is
EXIT_REASON_BUS_LOCK. It is non-deterministic hardware behavior. Dealing
with KVM_RUN_X86_BUS_LOCK in handle_bus_lock_vmexit could be redundant
when exit_reason.basic is EXIT_REASON_BUS_LOCK.

We can remove redundant handling of bus lock vmexit. Set
exit_reason.bus_lock_detected (bit 26) unconditionally, and deal with
KVM_RUN_X86_BUS_LOCK only in vmx_handle_exit.

Signed-off-by: Hao Xiang <hao.xiang@...ux.alibaba.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/vmx/vmx.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0c2c0d5..f993c38 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5561,9 +5561,13 @@ static int handle_encls(struct kvm_vcpu *vcpu)
 
 static int handle_bus_lock_vmexit(struct kvm_vcpu *vcpu)
 {
-	vcpu->run->exit_reason = KVM_EXIT_X86_BUS_LOCK;
-	vcpu->run->flags |= KVM_RUN_X86_BUS_LOCK;
-	return 0;
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+
+	/* The dedicated flag (bit 26 of exit reason in vmcs field) may or may
+	 * not be set by hardware.
+	 */
+	vmx->exit_reason.bus_lock_detected = true;
+	return 1;
 }
 
 /*
@@ -6050,9 +6054,8 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t exit_fastpath)
 	int ret = __vmx_handle_exit(vcpu, exit_fastpath);
 
 	/*
-	 * Even when current exit reason is handled by KVM internally, we
-	 * still need to exit to user space when bus lock detected to inform
-	 * that there is a bus lock in guest.
+	 * Exit to user space when bus lock detected to inform that there is
+	 * a bus lock in guest.
 	 */
 	if (to_vmx(vcpu)->exit_reason.bus_lock_detected) {
 		if (ret > 0)
-- 
1.8.3.1