kvm_vcpu_check_block() is called while not in TASK_RUNNING, and therefore
it cannot sleep. Writing to guest memory is therefore forbidden, but it
can happen on AMD processors if kvm_check_nested_events() causes a vmexit.
Fortunately, all events that are caught by kvm_check_nested_events() are
also recognized by kvm_vcpu_has_events() through vendor callbacks such as
kvm_x86_interrupt_allowed() or kvm_x86_ops.nested_ops->has_events(), so
remove the call and postpone the actual processing to vcpu_block().
Opportunistically honor the return of kvm_check_nested_events(). KVM
punted on the check in kvm_vcpu_running() because the only error path is
if vmx_complete_nested_posted_interrupt() fails, in which case KVM exits
to userspace with "internal error" i.e. the VM is likely dead anyways so
it wasn't worth overloading the return of kvm_vcpu_running().
Add the check mostly so that KVM is consistent with itself; the return of
the call via kvm_apic_accept_events()=>kvm_check_nested_events() that
immediately follows _is_ checked.
Reported-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
[sean: check and handle return of kvm_check_nested_events()]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dcc675d4e44b..8aeacbc2bff9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10815,6 +10815,17 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu)
return 1;
}
+ /*
+ * Evaluate nested events before exiting the halted state. This allows
+ * the halt state to be recorded properly in the VMCS12's activity
+ * state field (AMD does not have a similar field and a VM-Exit always
+ * causes a spurious wakeup from HLT).
+ */
+ if (is_guest_mode(vcpu)) {
+ if (kvm_check_nested_events(vcpu) < 0)
+ return 0;
+ }
+
if (kvm_apic_accept_events(vcpu) < 0)
return 0;
switch(vcpu->arch.mp_state) {
@@ -10837,9 +10848,6 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu)
static inline bool kvm_vcpu_running(struct kvm_vcpu *vcpu)
{
- if (is_guest_mode(vcpu))
- kvm_check_nested_events(vcpu);
-
return (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
!vcpu->arch.apf.halted);
}
This commit breaks delivery of a (virtualized) posted interrupt from
an L1 vCPU to a halted L2 vCPU.
Looking back at commit e6c67d8cf117 ("KVM: nVMX: Wake blocked vCPU in
guest-mode if pending interrupt in virtual APICv"), Liran wrote:
Note that this also handles the case of nested posted-interrupt by the
fact RVI is updated in vmx_complete_nested_posted_interrupt() which is
called from kvm_vcpu_check_block() -> kvm_arch_vcpu_runnable() ->
kvm_vcpu_running() -> vmx_check_nested_events() ->
vmx_complete_nested_posted_interrupt().
Clearly, that is no longer the case.
