Messages in this thread | | | Date | Thu, 13 Mar 2014 15:52:06 +0200 | From | Gleb Natapov <> | Subject | Re: [PATCH] KVM: SVM: fix cr8 intercept window |
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On Wed, Mar 12, 2014 at 06:20:01PM +0100, Paolo Bonzini wrote: > Il 12/03/2014 11:40, Radim Krčmář ha scritto: > >2014-03-11 22:05-0300, Marcelo Tosatti: > >>On Tue, Mar 11, 2014 at 07:11:18PM +0100, Radim Krčmář wrote: > >>>We always disable cr8 intercept in its handler, but only re-enable it > >>>if handling KVM_REQ_EVENT, so there can be a window where we do not > >>>intercept cr8 writes, which allows an interrupt to disrupt a higher > >>>priority task. > >>> > >>>Fix this by disabling intercepts in the same function that re-enables > >>>them when needed. This fixes BSOD in Windows 2008. > >>> > >>>Cc: <stable@vger.kernel.org> > >>>Signed-off-by: Radim Krčmář <rkrcmar@redhat.com> > >>>--- > >>> arch/x86/kvm/svm.c | 6 +++--- > >>> 1 file changed, 3 insertions(+), 3 deletions(-) > >>> > >>>diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > >>>index 64d9bb9..f676c18 100644 > >>>--- a/arch/x86/kvm/svm.c > >>>+++ b/arch/x86/kvm/svm.c > >>>@@ -3003,10 +3003,8 @@ static int cr8_write_interception(struct vcpu_svm *svm) > >>> u8 cr8_prev = kvm_get_cr8(&svm->vcpu); > >>> /* instruction emulation calls kvm_set_cr8() */ > >>> r = cr_interception(svm); > >>>- if (irqchip_in_kernel(svm->vcpu.kvm)) { > >>>- clr_cr_intercept(svm, INTERCEPT_CR8_WRITE); > >>>+ if (irqchip_in_kernel(svm->vcpu.kvm)) > >>> return r; > >>>- } > > I think that the old code here makes little sense, and for two reasons: > I agree that old code is wrong and the patch looks correct, but I only see how the bug may cause pending IRR to not be delivered in time, not how interrupt can disrupt a higher priority task.
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