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Date:   Thu, 8 Nov 2018 17:04:05 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Jann Horn <jannh@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rich Felker <dalias@libc.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Jethro Beekman <jethro@fortanix.com>,
        Florian Weimer <fweimer@redhat.com>,
        Linux API <linux-api@vger.kernel.org>, X86 ML <x86@kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.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>,
        Carlos O'Donell <carlos@redhat.com>,
        adhemerval.zanella@linaro.org
Subject: Re: RFC: userspace exception fixups
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On Wed, Nov 07, 2018 at 12:56:58PM -0800, Dave Hansen wrote:
> On 11/7/18 11:01 AM, Sean Christopherson wrote:
> > Going off comments in similar code related to UMIP, we'd need to figure
> > out how to handle protection keys.
> 
> There are two options:
> 1. Don't depend on the userspace mapping.  Do get_user_pages() to find
>    the instruction in the kernel direct map, and use that.
> 2. Do a WRPKRU that allows read access, do the read, then put PKRU back.
>    This is a pain because of preemption and all that jazz.
> 
> Right now, we just let the prefetch instruction detection fail if you
> mark it unreadable with pkeys.  Tough cookies, basically.  But, that's
> just the kernel being nice, but you need it for functionality, so it's
> tougher.

I would go with one because it is the stable way to do it and we are
100% sure to not conflict with pk's.

/Jarkko