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Date: Fri, 2 Dec 2016 18:07:26 +0100
From: Greg KH <gregkh@linuxfoundation.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: stable@vger.kernel.org, Matthew Whitehead <tedheadster@gmail.com>,
        Jiri Slaby <jslaby@suse.cz>, Willy Tarreau <w@1wt.eu>,
        "H . Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH BACKPORT v2 3.4 - 4.5] x86/traps: Ignore high word of
 regs->cs in early_idt_handler_common
Message-ID: <20161202170726.GA7340@kroah.com>
References: <e0022be5c4b69b8e5281ea0712a3059e89c0130f.1480538176.git.luto@kernel.org>
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On Thu, Dec 01, 2016 at 09:26:42AM -0800, Andy Lutomirski wrote:
> This is a backport of:
> commit fc0e81b2bea0ebceb71889b61d2240856141c9ee 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 commits:
> 
>   1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4")
>   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. ]

Thanks for the backport, now queued up for 4.4-stable.

greg k-h