From 81715d1ed45e4f5838059d39726dcfe40dc10c01 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Date: Tue, 23 Oct 2018 16:31:38 +0200 Subject: [PATCH] Revert "kvm: x86: optimize dr6 restore" MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This reverts commit 2d1f297f16c345cdf71d3ff43f25b93346248eab. As Christian Ehrhardt noted: The most common case is that vcpu->arch.dr6 and the host's %dr6 value are not related at all because ->switch_db_regs is zero. To do this all correctly, we must handle the case where the guest leaves an arbitrary unused value in vcpu->arch.dr6 before disabling breakpoints again. However, this means that vcpu->arch.dr6 is not suitable to detect the need for a %dr6 clear. Signed-off-by: Radim Krčmář --- arch/x86/kvm/x86.c | 13 ++++--------- 1 file changed, 4 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index bdcb5babfb68c..66d66d77caee5 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3271,16 +3271,11 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) kvm_x86_ops->vcpu_put(vcpu); vcpu->arch.last_host_tsc = rdtsc(); /* - * 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. + * 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. */ - if (vcpu->arch.dr6) - set_debugreg(0, 6); + set_debugreg(0, 6); } static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu, -- 2.39.5