| Message ID | 1511108743-11752-1-git-send-email-liran.alon@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 19/11/2017 17:25, Liran Alon wrote: > kvm_clear_exception_queue() should clear pending exception. > This also includes exceptions which were only marked pending but not > yet injected. This is because exception.pending is used for both L1 > and L2 to determine if an exception should be raised to guest. > Note that an exception which is pending but not yet injected will > be raised again once the guest will be resumed. > > Consider the following scenario: > 1) L0 KVM with ignore_msrs=false. > 2) L1 prepare vmcs12 with the following: > a) No intercepts on MSR (MSR_BITMAP exist and is filled with 0). > b) No intercept for #GP. > c) vmx-preemption-timer is configured. > 3) L1 enters into L2. > 4) L2 reads an unhandled MSR that exists in MSR_BITMAP > (such as 0x1fff). > > L2 RDMSR could be handled as described below: > 1) L2 exits to L0 on RDMSR and calls handle_rdmsr(). > 2) handle_rdmsr() calls kvm_inject_gp() which sets > KVM_REQ_EVENT, exception.pending=true and exception.injected=false. > 3) vcpu_enter_guest() consumes KVM_REQ_EVENT and calls > inject_pending_event() which calls vmx_check_nested_events() > which sees that exception.pending=true but > nested_vmx_check_exception() returns 0 and therefore does nothing at > this point. However let's assume it later sees vmx-preemption-timer > expired and therefore exits from L2 to L1 by calling > nested_vmx_vmexit(). > 4) nested_vmx_vmexit() calls prepare_vmcs12() > which calls vmcs12_save_pending_event() but it does nothing as > exception.injected is false. Also prepare_vmcs12() calls > kvm_clear_exception_queue() which does nothing as > exception.injected is already false. > 5) We now return from vmx_check_nested_events() with 0 while still > having exception.pending=true! > 6) Therefore inject_pending_event() continues > and we inject L2 exception to L1!... > > This commit will fix above issue by changing step (4) to > clear exception.pending in kvm_clear_exception_queue(). > > Fixes: 664f8e26b00c ("KVM: X86: Fix loss of exception which has not > yet been injected") > > Signed-off-by: Liran Alon <liran.alon@oracle.com> > Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com> > Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com> > Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com> > --- > arch/x86/kvm/vmx.c | 1 - > arch/x86/kvm/x86.h | 1 + > 2 files changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 7c3522a989d0..bee08782c781 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -11035,7 +11035,6 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr) > if (vmx->nested.nested_run_pending) > return -EBUSY; > nested_vmx_inject_exception_vmexit(vcpu, exit_qual); > - vcpu->arch.exception.pending = false; > return 0; > } > > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h > index d0b95b7a90b4..6d112d8f799c 100644 > --- a/arch/x86/kvm/x86.h > +++ b/arch/x86/kvm/x86.h > @@ -12,6 +12,7 @@ > > static inline void kvm_clear_exception_queue(struct kvm_vcpu *vcpu) > { > + vcpu->arch.exception.pending = false; > vcpu->arch.exception.injected = false; > } > > Finally queued, thanks. Paolo
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 7c3522a989d0..bee08782c781 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -11035,7 +11035,6 @@ static int vmx_check_nested_events(struct kvm_vcpu *vcpu, bool external_intr) if (vmx->nested.nested_run_pending) return -EBUSY; nested_vmx_inject_exception_vmexit(vcpu, exit_qual); - vcpu->arch.exception.pending = false; return 0; } diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h index d0b95b7a90b4..6d112d8f799c 100644 --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -12,6 +12,7 @@ static inline void kvm_clear_exception_queue(struct kvm_vcpu *vcpu) { + vcpu->arch.exception.pending = false; vcpu->arch.exception.injected = false; }
kvm_clear_exception_queue() should clear pending exception. This also includes exceptions which were only marked pending but not yet injected. This is because exception.pending is used for both L1 and L2 to determine if an exception should be raised to guest. Note that an exception which is pending but not yet injected will be raised again once the guest will be resumed. Consider the following scenario: 1) L0 KVM with ignore_msrs=false. 2) L1 prepare vmcs12 with the following: a) No intercepts on MSR (MSR_BITMAP exist and is filled with 0). b) No intercept for #GP. c) vmx-preemption-timer is configured. 3) L1 enters into L2. 4) L2 reads an unhandled MSR that exists in MSR_BITMAP (such as 0x1fff). L2 RDMSR could be handled as described below: 1) L2 exits to L0 on RDMSR and calls handle_rdmsr(). 2) handle_rdmsr() calls kvm_inject_gp() which sets KVM_REQ_EVENT, exception.pending=true and exception.injected=false. 3) vcpu_enter_guest() consumes KVM_REQ_EVENT and calls inject_pending_event() which calls vmx_check_nested_events() which sees that exception.pending=true but nested_vmx_check_exception() returns 0 and therefore does nothing at this point. However let's assume it later sees vmx-preemption-timer expired and therefore exits from L2 to L1 by calling nested_vmx_vmexit(). 4) nested_vmx_vmexit() calls prepare_vmcs12() which calls vmcs12_save_pending_event() but it does nothing as exception.injected is false. Also prepare_vmcs12() calls kvm_clear_exception_queue() which does nothing as exception.injected is already false. 5) We now return from vmx_check_nested_events() with 0 while still having exception.pending=true! 6) Therefore inject_pending_event() continues and we inject L2 exception to L1!... This commit will fix above issue by changing step (4) to clear exception.pending in kvm_clear_exception_queue(). Fixes: 664f8e26b00c ("KVM: X86: Fix loss of exception which has not yet been injected") Signed-off-by: Liran Alon <liran.alon@oracle.com> Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com> Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com> Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com> --- arch/x86/kvm/vmx.c | 1 - arch/x86/kvm/x86.h | 1 + 2 files changed, 1 insertion(+), 1 deletion(-)