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From: hpa@zytor.com
To: Denys Vlasenko <dvlasenk@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Julien Thierry <julien.thierry@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Ingo Molnar <mingo@kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	James Morse <james.morse@arm.com>,
	valentin.schneider@arm.com, Brian Gerst <brgerst@gmail.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Andrew Lutomirski <luto@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 01/25] x86: Make SMAP 64-bit only
Date: Thu, 21 Mar 2019 11:18:05 -0700	[thread overview]
Message-ID: <33D32634-51DC-426D-BE4A-F78B862760D5@zytor.com> (raw)
In-Reply-To: <aac45ef8-0196-b1c4-67ce-26dd0da6d641@redhat.com>

On March 21, 2019 10:25:05 AM PDT, Denys Vlasenko <dvlasenk@redhat.com> wrote:
>On 3/18/19 7:10 PM, Linus Torvalds wrote:
>> On Mon, Mar 18, 2019 at 10:51 AM Peter Zijlstra
><peterz@infradead.org> wrote:
>>>
>>> How about I do a patch that schedules EFLAGS for both 32bit and
>64bit,
>>> mark this for backporting to infinity.
>>>
>>> And then at the end, after the objtool-ac bits land, I do a patch
>>> removing the EFLAGS scheduling for x86_64.
>> 
>> Sounds sane to me.
>> 
>> And we can make it AC-conditional if it's actually shown to be
>visible
>> from a performance standpoint.
>> 
>> But iirc pushf/popf isn't really that expensive - in fact I think
>it's
>> pretty cheap when system flags don't change.
>
>I did not see evidence of this. In my testing,
>POPF is always ~20 cycles, even if popped flags are identical to
>current
>state of flags.

I think you will find that if you change system flags it is much slower.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

  reply	other threads:[~2019-03-21 18:19 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-18 15:38 [PATCH 00/25] objtool: UACCESS validation v4 Peter Zijlstra
2019-03-18 15:38 ` [PATCH 01/25] x86: Make SMAP 64-bit only Peter Zijlstra
2019-03-18 16:58   ` Linus Torvalds
2019-03-18 17:36     ` Peter Zijlstra
2019-03-18 17:51       ` Peter Zijlstra
2019-03-18 18:10         ` Linus Torvalds
2019-03-21 17:12           ` hpa
2019-03-21 17:25           ` Denys Vlasenko
2019-03-21 18:18             ` hpa [this message]
2019-03-21 21:03               ` Peter Zijlstra
2019-03-21 18:21             ` Linus Torvalds
2019-03-19 11:16   ` [PATCH 01/25] sched/x86: Save [ER]FLAGS on context switch Peter Zijlstra
2019-03-18 15:38 ` [PATCH 02/25] tracing: Improve "if" macro code generation Peter Zijlstra
2019-03-18 17:41   ` Steven Rostedt
2019-03-18 23:37   ` Josh Poimboeuf
2019-03-19 10:11     ` Peter Zijlstra
2019-03-20 11:18   ` David Laight
2019-03-20 17:26     ` Linus Torvalds
2019-03-20 17:37       ` David Laight
2019-03-20 17:38         ` Linus Torvalds
2019-03-20 18:18       ` Steven Rostedt
2019-05-09 13:00       ` Steven Rostedt
2019-05-09 16:51         ` Linus Torvalds
2019-05-09 18:29           ` Steven Rostedt
2019-05-09 18:45             ` Josh Poimboeuf
2019-05-09 18:47               ` Josh Poimboeuf
2019-05-09 18:48                 ` Randy Dunlap
2019-05-09 18:57                   ` Josh Poimboeuf
2019-05-09 19:06               ` Steven Rostedt
2019-05-09 19:28                 ` Steven Rostedt
2019-05-09 19:44                   ` Linus Torvalds
2019-03-18 15:38 ` [PATCH 03/25] x86/ia32: Fix ia32_restore_sigcontext AC leak Peter Zijlstra
2019-03-18 15:38 ` [PATCH 04/25] i915,uaccess: Fix redundant CLAC Peter Zijlstra
2019-03-18 15:38 ` [PATCH 05/25] x86/uaccess: Move copy_user_handle_tail into asm Peter Zijlstra
2019-03-18 15:38 ` [PATCH 06/25] x86/uaccess: Fix up the fixup Peter Zijlstra
2019-03-18 15:38 ` [PATCH 07/25] x86/nospec,objtool: Introduce ANNOTATE_IGNORE_ALTERNATIVE Peter Zijlstra
2019-03-18 15:38 ` [PATCH 08/25] x86/uaccess,xen: Suppress SMAP warnings Peter Zijlstra
2019-03-18 15:38 ` [PATCH 09/25] x86/uaccess: Always inline user_access_begin() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 10/25] x86/uaccess,signal: Fix AC=1 bloat Peter Zijlstra
2019-03-18 15:38 ` [PATCH 11/25] x86/uaccess: Introduce user_access_{save,restore}() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 12/25] x86/smap: Ditch __stringify() Peter Zijlstra
2019-03-18 15:38 ` [PATCH 13/25] x86/uaccess,kasan: Fix KASAN vs SMAP Peter Zijlstra
2019-03-18 15:38 ` [PATCH 14/25] x86/uaccess,ubsan: Fix UBSAN " Peter Zijlstra
2019-03-18 15:38 ` [PATCH 15/25] x86/uaccess,ftrace: Fix ftrace_likely_update() " Peter Zijlstra
2019-03-18 15:38 ` [PATCH 16/25] x86/uaccess,kcov: Disable stack protector Peter Zijlstra
2019-03-18 15:38 ` [PATCH 17/25] objtool: Set insn->func for alternatives Peter Zijlstra
2019-03-18 15:38 ` [PATCH 18/25] objtool: Handle function aliases Peter Zijlstra
2019-03-18 15:38 ` [PATCH 19/25] objtool: Rewrite add_ignores() Peter Zijlstra
2019-03-18 15:39 ` [PATCH 20/25] objtool: Add --backtrace support Peter Zijlstra
2019-03-18 15:39 ` [PATCH 21/25] objtool: Rewrite alt->skip_orig Peter Zijlstra
2019-03-18 15:39 ` [PATCH 22/25] objtool: Fix sibling call detection Peter Zijlstra
2019-03-18 15:39 ` [PATCH 23/25] objtool: Add UACCESS validation Peter Zijlstra
2019-03-18 23:51   ` Josh Poimboeuf
2019-05-07 11:52   ` Peter Zijlstra
2019-03-18 15:39 ` [PATCH 24/25] objtool: uaccess PUSHF/POPF support Peter Zijlstra
2019-03-18 15:39 ` [PATCH 25/25] objtool: Add Direction Flag validation Peter Zijlstra
2019-03-18 23:57 ` [PATCH 00/25] objtool: UACCESS validation v4 Josh Poimboeuf
2019-03-19 11:20   ` Peter Zijlstra
2019-03-19 11:17 ` [PATCH 26/25] sched/x86_64: Don't save flags on context switch Peter Zijlstra

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