KVM: Use thread debug register storage instead of kvm specific data

Instead of saving the debug registers from the processor to a kvm data
structure, rely in the debug registers stored in the thread structure.
This allows us not to save dr6 and dr7.

Reduces lightweight vmexit cost by 350 cycles, or 11 percent.

Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 33901be75a36cb11a73254ebd63aa9a39ae9d7e4..e8f166a02c79c6a978391acb6ae892507358f09d 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -362,9 +362,6 @@ struct kvm_vcpu_arch {
        u32 pat;
 
        int switch_db_regs;
-       unsigned long host_db[KVM_NR_DB_REGS];
-       unsigned long host_dr6;
-       unsigned long host_dr7;
        unsigned long db[KVM_NR_DB_REGS];
        unsigned long dr6;
        unsigned long dr7;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 35e7fc54de35d818ab3cde6ff8d9172b444bc8a5..3e893c4fdd39989f57b335f6efbb95906419e41d 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3623,14 +3623,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 
        kvm_guest_enter();
 
-       get_debugreg(vcpu->arch.host_dr6, 6);
-       get_debugreg(vcpu->arch.host_dr7, 7);
        if (unlikely(vcpu->arch.switch_db_regs)) {
-               get_debugreg(vcpu->arch.host_db[0], 0);
-               get_debugreg(vcpu->arch.host_db[1], 1);
-               get_debugreg(vcpu->arch.host_db[2], 2);
-               get_debugreg(vcpu->arch.host_db[3], 3);
-
                set_debugreg(0, 7);
                set_debugreg(vcpu->arch.eff_db[0], 0);
                set_debugreg(vcpu->arch.eff_db[1], 1);
@@ -3641,15 +3634,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
        trace_kvm_entry(vcpu->vcpu_id);
        kvm_x86_ops->run(vcpu, kvm_run);
 
-       if (unlikely(vcpu->arch.switch_db_regs)) {
-               set_debugreg(0, 7);
-               set_debugreg(vcpu->arch.host_db[0], 0);
-               set_debugreg(vcpu->arch.host_db[1], 1);
-               set_debugreg(vcpu->arch.host_db[2], 2);
-               set_debugreg(vcpu->arch.host_db[3], 3);
+       if (unlikely(vcpu->arch.switch_db_regs || test_thread_flag(TIF_DEBUG))) {
+               set_debugreg(current->thread.debugreg0, 0);
+               set_debugreg(current->thread.debugreg1, 1);
+               set_debugreg(current->thread.debugreg2, 2);
+               set_debugreg(current->thread.debugreg3, 3);
+               set_debugreg(current->thread.debugreg6, 6);
+               set_debugreg(current->thread.debugreg7, 7);
        }
-       set_debugreg(vcpu->arch.host_dr6, 6);
-       set_debugreg(vcpu->arch.host_dr7, 7);
 
        set_bit(KVM_REQ_KICK, &vcpu->requests);
        local_irq_enable();