linux-kernel - Re: [patch 01/10] x86/fpu/signal: Clarify exception handling in restore_fpregs_from

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Date:   Thu, 02 Sep 2021 16:08:05 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jarkko Sakkinen <jarkko@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [patch 01/10] x86/fpu/signal: Clarify exception handling in
 restore_fpregs_from_user()

On Thu, Sep 02 2021 at 16:08, Jarkko Sakkinen wrote:
> On Wed, 2021-09-01 at 16:47 +0000, Sean Christopherson wrote:
>> 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.

I understood that storing the trap number is useful. I was just
questioning the #MC angle. I.e. pretending that the #MC caused by ENCLS
is recoverable.

Thanks,

        tglx