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@xxxxxxxxxxxxxxx>
> > Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> > ---
> > 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;
> > - }
> > if (cr8_prev <= kvm_get_cr8(&svm->vcpu))
> > return r;
> > kvm_run->exit_reason = KVM_EXIT_SET_TPR;
> > @@ -3568,6 +3566,8 @@ static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
> > if (is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK))
> > return;
> >
> > + clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
> > +
> > if (irr == -1)
> > return;
>
> Shouldnt IRR be injected if TPR < IRR ? (via KVM_REQ_EVENT).
>
> 1) IRR has interrupt 10.
> 2) TPR now 9 due to CR8 write.
> 3) 10 should be injected.
Definitely should, and we will set KVM_REQ_EVENT through kvm_set_cr8()
if we lower the TPR.
(I checked that the bug isn't in apic_update_ppr().)
> Also not clearing the intercept can cause continuous CR8 writes to
> exit until KVM_REQ_EVENT ?
It is intended, I suppose this is because we run with V_INTR_MASKING, so
writes to CR8 only affect V_TPR register; guest then raises it once more
and APIC incorrectly gives us low priority interrupt.
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