On Friday, 2021-07-09 at 15:47:08 UTC, Sean Christopherson wrote:
> 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.
Okay.
>> } emulation_failure;
>> /* KVM_EXIT_OSI */
>> struct {
>> --
>> 2.30.2
>>
dme.
--
What did you learn today? I learnt nothing.
