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Date: Thu, 1 Dec 2016 15:51:24 +0100
From: Willy Tarreau <w@1wt.eu>
To: Andy Lutomirski <luto@kernel.org>
Cc: stable@vger.kernel.org, Matthew Whitehead <tedheadster@gmail.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH BACKPORT 3.4 - 4.5] x86/traps: Ignore high word of
 regs->cs in early_idt_handler_common
Message-ID: <20161201145124.GA17630@1wt.eu>
References: <e0022be5c4b69b8e5281ea0712a3059e89c0130f.1480538175.git.luto@kernel.org>
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On Wed, Nov 30, 2016 at 12:37:53PM -0800, Andy Lutomirski wrote:
> This is a backport of:
> commit cb32c69920e58a1a58e7b5cad975038a69c0ce7d upstream
> 
> On the 80486 DX, it seems that some exceptions may leave garbage in
> the high bits of CS.  This causes sporadic failures in which
> early_fixup_exception() refuses to fix up an exception.
> 
> As far as I can tell, this has been buggy for a long time, but the
> problem seems to have been exacerbated by commit 1e02ce4cccdc ("x86:
> Store a per-cpu shadow copy of CR4") and commit e1bfc11c5a6f
> ("x86/init: Fix cr4_init_shadow() on CR4-less machines").
> 
> This appears to have broken for as long as we've had early
> exception handling.
> 
> [ This backport should apply to kernels from 3.4 - 4.5. ]

This morning before coffee took effect I read 3.4-3.5 so I classed
it, now I've queued it for 3.10.

Thanks Andy!
Willy