Messages in this thread | | | Subject | Re: [patch 01/10] x86/fpu/signal: Clarify exception handling in restore_fpregs_from_user() | From | Jarkko Sakkinen <> | Date | Thu, 02 Sep 2021 16:08:11 +0300 |
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On Wed, 2021-09-01 at 16:47 +0000, Sean Christopherson wrote: > On Wed, Sep 01, 2021, Thomas Gleixner wrote: > > On Wed, Sep 01 2021 at 14:00, Thomas Gleixner wrote: > > > commit b2f9d678e28c ("x86/mce: Check for faults tagged in > > > EXTABLE_CLASS_FAULT exception table entries") made use of this in MCE to > > > allow in kernel recovery. The only thing it uses is checking the > > > exception handler type. > > > > > > Bah. I'll fix that up to make that less obscure. > > > > > > The remaining two use cases (SGX and FPU) make use of the stored trap > > > number. > > > > Though while for the FPU use case we really want to handle the #MC case, > > it's not clear to me whether this is actually correct for SGX. > > > > Jarkko, Sean, Dave? > > Are you asking about #MC specifically, or about SGX consuming the trap number in > general? > > For #MC, it's probably a moot point because #MC on ENCLS is not recoverable for > current hardware. If #MC somehow occurs on ENCLS and doesn't kill the platform, > "handling" the #MC in SGX is probably wrong. Note, Tony is working on a series to > support recoverable #MC on SGX stuff on future hardware[*], but I'm not sure that's > relevant to this discussion. > > As for SGX consuming the trap number in general, it's correct. For non-KVM usage, > it's nice to have but not strictly necessary. Any fault except #PF on ENCLS is > guaranteed to be a kernel or hardware bug; SGX uses the trap number to WARN on a > !#PF exception, e.g. on #GP or #UD. Not having the trap number would mean losing > those sanity checks, which have been useful in the past.
AFAIK, we do not consider #UD as a bug. Agree with the conclusion that SGX should never #MC, I just did not get this part. #UD is something that is useful for SGX run-time.
/Jarkko
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