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KVM: nSVM: do not forward NMI window singlestep VM exits to L1

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Nested hypervisor should not see singlestep VM exits if singlestepping
was enabled internally by KVM. Windows is particularly sensitive to this
and known to bluescreen on unexpected VM exits.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Ladi Prosek 2017-06-21 09:06:58 +02:00 committed by Paolo Bonzini
parent 4aebd0e9ca
commit ab2f4d73eb
1 changed files with 40 additions and 5 deletions
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45
arch/x86/kvm/svm.c
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@ -189,6 +189,7 @@ struct vcpu_svm {
struct nested_state nested;
bool nmi_singlestep;
u64 nmi_singlestep_guest_rflags;
unsigned int3_injected;
unsigned long int3_rip;
@ -966,9 +967,13 @@ static void svm_disable_lbrv(struct vcpu_svm *svm)
static void disable_nmi_singlestep(struct vcpu_svm *svm)
{
svm->nmi_singlestep = false;
if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP))
svm->vmcb->save.rflags &=
~(X86_EFLAGS_TF | X86_EFLAGS_RF);
if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP)) {
/* Clear our flags if they were not set by the guest */
if (!(svm->nmi_singlestep_guest_rflags & X86_EFLAGS_TF))
svm->vmcb->save.rflags &= ~X86_EFLAGS_TF;
if (!(svm->nmi_singlestep_guest_rflags & X86_EFLAGS_RF))
svm->vmcb->save.rflags &= ~X86_EFLAGS_RF;
}
}
/* Note:
@ -2538,6 +2543,31 @@ static int nested_svm_exit_handled_msr(struct vcpu_svm *svm)
return (value & mask) ? NESTED_EXIT_DONE : NESTED_EXIT_HOST;
}
/* DB exceptions for our internal use must not cause vmexit */
static int nested_svm_intercept_db(struct vcpu_svm *svm)
{
unsigned long dr6;
/* if we're not singlestepping, it's not ours */
if (!svm->nmi_singlestep)
return NESTED_EXIT_DONE;
/* if it's not a singlestep exception, it's not ours */
if (kvm_get_dr(&svm->vcpu, 6, &dr6))
return NESTED_EXIT_DONE;
if (!(dr6 & DR6_BS))
return NESTED_EXIT_DONE;
/* if the guest is singlestepping, it should get the vmexit */
if (svm->nmi_singlestep_guest_rflags & X86_EFLAGS_TF) {
disable_nmi_singlestep(svm);
return NESTED_EXIT_DONE;
}
/* it's ours, the nested hypervisor must not see this one */
return NESTED_EXIT_HOST;
}
static int nested_svm_exit_special(struct vcpu_svm *svm)
{
u32 exit_code = svm->vmcb->control.exit_code;
@ -2593,8 +2623,12 @@ static int nested_svm_intercept(struct vcpu_svm *svm)
}
case SVM_EXIT_EXCP_BASE ... SVM_EXIT_EXCP_BASE + 0x1f: {
u32 excp_bits = 1 << (exit_code - SVM_EXIT_EXCP_BASE);
if (svm->nested.intercept_exceptions & excp_bits)
vmexit = NESTED_EXIT_DONE;
if (svm->nested.intercept_exceptions & excp_bits) {
if (exit_code == SVM_EXIT_EXCP_BASE + DB_VECTOR)
vmexit = nested_svm_intercept_db(svm);
else
vmexit = NESTED_EXIT_DONE;
}
/* async page fault always cause vmexit */
else if ((exit_code == SVM_EXIT_EXCP_BASE + PF_VECTOR) &&
svm->apf_reason != 0)
@ -4635,6 +4669,7 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu)
* Something prevents NMI from been injected. Single step over possible
* problem (IRET or exception injection or interrupt shadow)
*/
svm->nmi_singlestep_guest_rflags = svm_get_rflags(vcpu);
svm->nmi_singlestep = true;
svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
}