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Subject: Re: [RFC][PATCH 1/8] x86/mm: clarify hardware vs. software "error_code"
From:   Andy Lutomirski <luto@amacapital.net>
In-Reply-To: <20180907194854.74729D71@viggo.jf.intel.com>
Date:   Fri, 7 Sep 2018 15:48:18 -0700
Cc:     linux-kernel@vger.kernel.org, sean.j.christopherson@intel.com,
        peterz@infradead.org, tglx@linutronix.de, x86@kernel.org,
        luto@kernel.org
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References: <20180907194852.3C351B82@viggo.jf.intel.com> <20180907194854.74729D71@viggo.jf.intel.com>
To:     Dave Hansen <dave.hansen@linux.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Sep 7, 2018, at 12:48 PM, Dave Hansen <dave.hansen@linux.intel.com> wro=
te:
>=20
>=20
> From: Dave Hansen <dave.hansen@linux.intel.com>
>=20
> We pass around a variable called "error_code" all around the page
> fault code.  Sounds simple enough, especially since "error_code" looks
> like it exactly matches the values that the hardware gives us on the
> stack to report the page fault error code (PFEC in SDM parlance).
>=20
> But, that's not how it works.
>=20
> For part of the page fault handler, "error_code" does exactly match
> PFEC.  But, during later parts, it diverges and starts to mean
> something a bit different.
>=20
> Give it two names for its two jobs.

How hard would it be to just remove sw_error_code instead?  It seems like it=
 adds little value and much confusion.

I=E2=80=99m also unconvinced that the warning is terribly useful. We=E2=80=99=
re going to oops when this happens anyway.

I=E2=80=99ll rebase my diagnostic patch on top of this series after it settl=
es.