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Subject: Re: [PATCH 6/9] x86/mm: Introduce ptep_set_wrprotect_flush and
 related functions
References: <20180607143705.3531-1-yu-cheng.yu@intel.com>
 <20180607143705.3531-7-yu-cheng.yu@intel.com>
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From: Dave Hansen <dave.hansen@linux.intel.com>
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Date: Thu, 7 Jun 2018 18:20:36 -0700
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To: Andy Lutomirski <luto@kernel.org>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>, LKML <linux-kernel@vger.kernel.org>, linux-doc@vger.kernel.org, Linux-MM <linux-mm@kvack.org>, linux-arch <linux-arch@vger.kernel.org>, X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. J. Lu" <hjl.tools@gmail.com>, "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@intel.com>, "Ravi V. Shankar" <ravi.v.shankar@intel.com>, Jonathan Corbet <corbet@lwn.net>, Oleg Nesterov <oleg@redhat.com>, Arnd Bergmann <arnd@arndb.de>, mike.kravetz@oracle.com

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.