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

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Date:   Wed, 1 Sep 2021 12:22:58 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>
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>,
        Jarkko Sakkinen <jarkko@...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 9/1/21 9:47 AM, 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.

Yeah, for bare-metal SGX, the trap number only determines if we get a
warning or not.  There's no attempt at recovery or any consequential
change in behavior due to the trap number (other than the warning).