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From: Denys Vlasenko <vda.linux@googlemail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>, 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, 9 Mar 2015 17:28:26 +0100	[thread overview]
Message-ID: <CAK1hOcNmfy3RS20t-+Pmn+KFtoYM+RqyCx=LgfcHaaXnzF1M5w@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFzck8nuV06AZhhFXgUQEsujZCtufw0jY4iswJUggh6ruA@mail.gmail.com>

On Mon, Mar 9, 2015 at 5:08 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Mar 9, 2015 at 7:05 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
>>     New:
>>      1e6:   0f ba 64 24 38 11       btl    $0x11,0x38(%esp)
>
> btl? Really?
>
> Why isn't that just
>
>     testb $2,0x3a(%esp)
>
> which is both smaller and quite a bit faster on older machines.

Ok. (I thought people won't be happy about this.)

> Or just at least *partially* do what we used to do, and make it all be
>
>     movb  PT_EFLAGS+2(%esp),%al
>     andb $2,%al
>     orb PT_CS(%esp),%al
>     testb $3,%al
>     je restore_nocheck

These insns must run serially. 4 cycles.

        test
        branch
        test
        branch

can execute both test/branch'es out-of-order in parallel.
2 cycles.

  reply	other threads:[~2015-03-09 16:28 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 [this message]
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
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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