Subject: Re: [PATCH RFC 3/4] x86/pti: don't mark the user PGD with _PAGE_NX.
To: Willy Tarreau <w@1wt.eu>
References: <1515427939-10999-1-git-send-email-w@1wt.eu>
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 <57039ac1-efe2-2f97-386f-dab0b90f64a5@intel.com>
 <20180108171707.GG10913@1wt.eu>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de,
        gnomes@lxorguk.ukuu.org.uk, torvalds@linux-foundation.org,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Borislav Petkov <bp@alien8.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Andy Lutomirski <luto@kernel.org>
From: Dave Hansen <dave.hansen@intel.com>
Message-ID: <407b4328-4447-38a5-15c1-0170741e3d14@intel.com>
Date: Mon, 8 Jan 2018 09:23:49 -0800
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On 01/08/2018 09:17 AM, Willy Tarreau wrote:
>> I think the prctl() should apply to an entire process, not to a thread.
> 
> As I mentionned in another mail, I didn't know how to do it, even less
> how to do it fast enough so that we didn't add more cycles to the syscall
> code.

You can _implement_ it with a task thread if you want.  Just spray it
across all threads at the prctl()-time instead of a single thread.
It'll take a wee bit of locking.

I just don't think the API should apply to a single thread.