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From: "H. Peter Anvin" <hpa@zytor.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Denys Vlasenko <vda.linux@googlemail.com>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Oleg Nesterov <oleg@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Alexei Starovoitov <ast@plumgrid.com>,
	Will Drewry <wad@chromium.org>, Kees Cook <keescook@chromium.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: entry_32.S: change ESPFIX test to not touch PT_OLDSS(%esp)
Date: Mon, 09 Mar 2015 12:26:49 -0700	[thread overview]
Message-ID: <54FDF3F9.50203@zytor.com> (raw)
In-Reply-To: <CALCETrViW_rhzYQ+re8=KMLtc=_4YDceWKLzCOk=ReEUbe+rfg@mail.gmail.com>

On 03/09/2015 12:13 PM, Andy Lutomirski wrote:
> On Mon, Mar 9, 2015 at 10:44 AM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 03/09/2015 09:44 AM, Linus Torvalds wrote:
>>>
>>> And remember: those zero-cost out-of-order branches turn quite
>>> expensive if they *ever* mispredict. Even a 5% mispredict rate is
>>> likely to mean "it's better to have a data dependency chain".
>>>
>>> So it could easily go either way. I'm not convinced the old code is bad at all.
>>>
>>
>> I'm inclined to side with Linus here.  I'm hesitant to change this based
>> on pure speculation.
>>
>> To answer Andy's question: I do believe we need espfix for V86 mode as well.
>>
> 
> I think we don't.  Did I screw up my test?
> 

I don't see how your test executes V86 mode code at all, since there
seems to be nothing mapped at the bottom of memory?

	-hpa



  reply	other threads:[~2015-03-09 19:27 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-09 14:05 Denys Vlasenko
2015-03-09 14:18 ` Andy Lutomirski
2015-03-09 15:00   ` Denys Vlasenko
2015-03-09 15:09     ` Andy Lutomirski
2015-03-09 19:31       ` Denys Vlasenko
2015-03-09 15:13     ` Ingo Molnar
2015-03-09 15:18       ` Andy Lutomirski
2015-03-09 15:47       ` Steven Rostedt
2015-03-09 15:54         ` Ingo Molnar
2015-03-09 16:08 ` Linus Torvalds
2015-03-09 16:28   ` Denys Vlasenko
2015-03-09 16:44     ` Linus Torvalds
2015-03-09 17:44       ` H. Peter Anvin
2015-03-09 19:13         ` Andy Lutomirski
2015-03-09 19:26           ` H. Peter Anvin [this message]
2015-03-09 19:51             ` Andy Lutomirski
2015-03-09 17:42   ` H. Peter Anvin
2015-03-09 17:45     ` Andy Lutomirski
2015-03-09 17:59       ` Linus Torvalds
2015-03-09 18:04         ` Andy Lutomirski
2015-03-09 18:16           ` Linus Torvalds
2015-03-09 18:32             ` Denys Vlasenko
2015-03-09 18:36             ` Andy Lutomirski
2015-03-10  6:25               ` Ingo Molnar

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