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
next prev parent 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 [PATCH] x86: entry_32.S: change ESPFIX test to not touch PT_OLDSS(%esp) 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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