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Date: Mon, 9 Mar 2015 11:16:03 -0700
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Subject: Re: [PATCH] x86: entry_32.S: change ESPFIX test to not touch PT_OLDSS(%esp)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Denys Vlasenko <dvlasenk@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@kernel.org>,
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        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
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On Mon, Mar 9, 2015 at 11:04 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>
> One option would be to change the NMI entry code to move itself down 8
> bytes if this happens (came from kernel mode or sp == sp0 - 12,
> perhaps).

Hmm. That whole code currently depends on the stack setup being just a
single instruction (the move to esp). And that simplifies things, I'd
like to keep it that way.

I'd *much* rather just keep the 8-byte padding. What was so
problematic with that? It worked. It's been around forever. Removing
it is the bug.

                        Linus