KVM: x86: never write to memory from kvm_vcpu_check_block()
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@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[sean: check and handle return of kvm_check_nested_events()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <
20220921003201.1441511-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>