linux-kernel - Re: [PATCH 6/9] x86/mm: Introduce ptep_set_wrprotect

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Date:   Thu, 7 Jun 2018 18:20:36 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. J. Lu" <hjl.tools@...il.com>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Oleg Nesterov <oleg@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        mike.kravetz@...cle.com
Subject: Re: [PATCH 6/9] x86/mm: Introduce ptep_set_wrprotect_flush and
 related functions

On 06/07/2018 05:59 PM, Andy Lutomirski wrote:
> Can you ask the architecture folks to clarify the situation?  And, if
> your notes are indeed correct, don't we need code to handle spurious
> faults?

I'll double check that I didn't misunderstand the situation and that it
has not changed on processors with shadow stacks.

But, as far as spurious faults, wouldn't it just be a fault because
we've transiently gone to Present=0?  We already do that when clearing
the Dirty bit, so I'm not sure that's new.  We surely already handle
that one.