linux-kernel - [RFC PATCH 2/3] kvm: x86: Use KVM_DEBUGREG_NEED_RELOAD instead of KVM_DEBUGREG_BP

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Date:   Thu, 16 Apr 2020 18:15:08 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        kvm@...r.kernel.org
Cc:     Nadav Amit <namit@...technion.ac.il>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: [RFC PATCH 2/3] kvm: x86: Use KVM_DEBUGREG_NEED_RELOAD instead of KVM_DEBUGREG_BP_ENABLED

Once any #BP enabled in DR7, it will set KVM_DEBUGREG_BP_ENABLED, which
leads to reload DRn before every VM entry even if none of DRn changed.

Drop KVM_DEBUGREG_BP_ENABLED flag and set KVM_DEBUGREG_NEED_RELOAD flag
for the cases that DRn need to be reloaded instead, to avoid unnecessary
DRn reload.

Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
---
 arch/x86/include/asm/kvm_host.h | 3 +--
 arch/x86/kvm/x86.c              | 4 ++--
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f465c76e6e5a..87e2d020351e 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -509,9 +509,8 @@ struct kvm_pmu {
 struct kvm_pmu_ops;
 
 enum {
-	KVM_DEBUGREG_BP_ENABLED = 1,
+	KVM_DEBUGREG_NEED_RELOAD = 1,
 	KVM_DEBUGREG_WONT_EXIT = 2,
-	KVM_DEBUGREG_NEED_RELOAD = 4,
 };
 
 struct kvm_mtrr_range {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cce926658d10..71264df64001 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1086,9 +1086,8 @@ static void kvm_update_dr7(struct kvm_vcpu *vcpu)
 	else
 		dr7 = vcpu->arch.dr7;
 	kvm_x86_ops.set_dr7(vcpu, dr7);
-	vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_BP_ENABLED;
 	if (dr7 & DR7_BP_EN_MASK)
-		vcpu->arch.switch_db_regs |= KVM_DEBUGREG_BP_ENABLED;
+		vcpu->arch.switch_db_regs |= KVM_DEBUGREG_NEED_RELOAD;
 }
 
 static u64 kvm_dr6_fixed(struct kvm_vcpu *vcpu)
@@ -1128,6 +1127,7 @@ static int __kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 		break;
 	}
 
+	vcpu->arch.switch_db_regs |= KVM_DEBUGREG_NEED_RELOAD;
 	return 0;
 }
 
-- 
2.20.1