KVM: x86: Deliver exception payload on KVM_GET_VCPU_EVENTS
KVM allows the deferral of exception payloads when a vCPU is in guest mode to allow the L1 hypervisor to intercept certain events (#PF, #DB) before register state has been modified. However, this behavior is incompatible with the KVM_{GET,SET}_VCPU_EVENTS ABI, as userspace expects register state to have been immediately modified. Userspace may opt-in for the payload deferral behavior with the KVM_CAP_EXCEPTION_PAYLOAD per-VM capability. As such, kvm_multiple_exception() will immediately manipulate guest registers if the capability hasn't been requested. Since the deferral is only necessary if a userspace ioctl were to be serviced at the same as a payload bearing exception is recognized, this behavior can be relaxed. Instead, opportunistically defer the payload from kvm_multiple_exception() and deliver the payload before completing a KVM_GET_VCPU_EVENTS ioctl. Signed-off-by: NOliver Upton <oupton@google.com> Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
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