[PATCH 3.2 174/200] KVM: SVM: fix cr8 intercept window

From: Ben Hutchings
Date: Sun Mar 30 2014 - 19:28:00 EST


3.2.56-rc1 review patch. If anyone has any objections, please let me know.

------------------

From: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>

commit 596f3142d2b7be307a1652d59e7b93adab918437 upstream.

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.

Signed-off-by: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Reviewed-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
arch/x86/kvm/svm.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2904,10 +2904,8 @@ static int cr8_write_interception(struct
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;
@@ -3462,6 +3460,8 @@ static void update_cr8_intercept(struct
if (is_guest_mode(vcpu) && (vcpu->arch.hflags & HF_VINTR_MASK))
return;

+ clr_cr_intercept(svm, INTERCEPT_CR8_WRITE);
+
if (irr == -1)
return;


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