On Tue, Jul 06, 2021, David Edmondson wrote:
> Should instruction emulation fail, include the VM exit reason in the
> emulation_failure data passed to userspace, in order that the VMM can
> report it as a debugging aid when describing the failure.
...
> @@ -7473,7 +7474,14 @@ static void prepare_emulation_failure_exit(struct kvm_vcpu *vcpu)
> memcpy(run->emulation_failure.insn_bytes,
> ctxt->fetch.data, insn_size);
> }
> +
> + run->emulation_failure.ndata = 4;
> + run->emulation_failure.flags |=
> + KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON;
> + run->emulation_failure.exit_reason =
> + static_call(kvm_x86_get_exit_reason)(vcpu);
> }
...
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index d9e4aabcb31a..863195371272 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -282,6 +282,7 @@ struct kvm_xen_exit {
>
> /* Flags that describe what fields in emulation_failure hold valid data. */
> #define KVM_INTERNAL_ERROR_EMULATION_FLAG_INSTRUCTION_BYTES (1ULL << 0)
> +#define KVM_INTERNAL_ERROR_EMULATION_FLAG_EXIT_REASON (1ULL << 1)
>
> /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
> struct kvm_run {
> @@ -404,6 +405,12 @@ struct kvm_run {
> __u64 flags;
> __u8 insn_size;
> __u8 insn_bytes[15];
> + /*
> + * The "exit reason" extracted from the
> + * VMCS/VMCB that was the cause of attempted
> + * emulation.
> + */
> + __u64 exit_reason;
Rather than providing just the exit reason and adding another kvm_x86_ops hook,
I would prefer to extend kvm_x86_get_exit_info() to also provide the exit reason
and use that. E.g. on VMX, all exceptions funnel through a single exit reason.
Dumping exit_info_{1,2} and error_code in addition to intr_info might not be all
that useful, but I can't see in harm either, and more info is generally a good
thing.
The only other user of kvm_x86_get_exit_info() is for tracepoints, those could
be modified to not pass in the exit reason.
> } emulation_failure;
> /* KVM_EXIT_OSI */
> struct {
> --
> 2.30.2
>
