diff options
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 20a667da0a31..92159db9cf71 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3186,11 +3186,16 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) kvm_x86_ops->vcpu_put(vcpu); vcpu->arch.last_host_tsc = rdtsc(); /* - * If userspace has set any breakpoints or watchpoints, dr6 is restored - * on every vmexit, but if not, we might have a stale dr6 from the - * guest. do_debug expects dr6 to be cleared after it runs, do the same. + * Here dr6 is either zero or, if the guest has run and userspace + * has not set any breakpoints or watchpoints, it can be set to + * the guest dr6 (stored in vcpu->arch.dr6). do_debug expects dr6 + * to be cleared after it runs, so clear the host register. However, + * MOV to DR can be expensive when running nested, omit it if + * vcpu->arch.dr6 is already zero: in that case, the host dr6 cannot + * currently be nonzero. */ - set_debugreg(0, 6); + if (vcpu->arch.dr6) + set_debugreg(0, 6); } static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu, |