From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Subject: Re: RFC: userspace exception fixups
Date: Sun, 18 Nov 2018 09:18:16 +0200
Message-ID: <20181118071816.GB4795@linux.intel.com>
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To: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>, "Christopherson, Sean J" <sean.j.christopherson@intel.com>, Jethro Beekman <jethro@fortanix.com>, Florian Weimer <fweimer@redhat.com>, Linux API <linux-api@vger.kernel.org>, Jann Horn <jannh@google.com>, Linus Torvalds <torvalds@linux-foundation.org>, X86 ML <x86@kernel.org>, linux-arch <linux-arch@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, Peter Zijlstra <peterz@infradead.org>, Rich Felker <dalias@libc.org>, nhorman@redhat.com, npmccallum@redhat.com, "Ayoun, Serge" <serge.ayoun@intel.com>, shay.katz-zamir@intel.com, linux-sgx@vger.kernel.org, Andy Shevchenko <andriy.shevchenko@linux.intel.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
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On Sun, Nov 18, 2018 at 09:15:48AM +0200, Jarkko Sakkinen wrote:
> On Thu, Nov 01, 2018 at 10:53:40AM -0700, Andy Lutomirski wrote:
> > Hi all-
> > 
> > The people working on SGX enablement are grappling with a somewhat
> > annoying issue: the x86 EENTER instruction is used from user code and
> > can, as part of its normal-ish operation, raise an exception.  It is
> > also highly likely to be used from a library, and signal handling in
> > libraries is unpleasant at best.
> > 
> > There's been some discussion of adding a vDSO entry point to wrap
> > EENTER and do something sensible with the exceptions, but I'm
> > wondering if a more general mechanism would be helpful.
> 
> I haven't really followed all of this discussion because I've been busy
> working on the patch set but for me all of these approaches look awfully
> complicated.
> 
> I'll throw my own suggestion and apologize if this has been already
> suggested and discarded: return-to-AEP.
> 
> My idea is to do just a small extension to SGX AEX handling. At the
> moment hardware will RAX, RBX and RCX with ERESUME parameters. We can
> fill extend this by filling other three spare registers with exception

s/fill extend/extend/

/Jarkko