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From: Borislav Petkov <bp@suse.de>
To: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Ingo Molnar <mingo@kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Pekka Riikonen <priikone@iki.fi>, Rik van Riel <riel@redhat.com>,
	Suresh Siddha <sbsiddha@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in xsave_user/xrestore_user
Date: Tue, 17 Mar 2015 10:47:50 +0100	[thread overview]
Message-ID: <20150317094750.GD18917@pd.tnic> (raw)
In-Reply-To: <20150316223743.GA14575@chrystal.uk.oracle.com>

On Mon, Mar 16, 2015 at 11:37:44PM +0100, Quentin Casasnovas wrote:

...

>   __user_insn("btl [var2], %0		\n\t",
>   	      , /* no outputs, no need for dummy arg */
> 	      SINGLE_ARG("r" (var1), [var2] "r" (var2)), /* two inputs */
> 	      "cc");

So this becomes pretty unreadable IMO. And we shouldn't go nuts with
optimizing this and sacrifice readability a lot.

TBH, I'd much prefer:

	if (static_cpu_has_safe(X86_FEATURE_XSAVEOPT)) {
		check_insn(XSAVEOPT, ...);
		return;
	}

	if (static_cpu_has_safe(X86_FEATURE_XSAVES)) {
		check_insn(XSAVES);
		return;
	}

	check_insn(XSAVE, ...)

which is pretty clear.

We can even go a step further and add a static_cpu_has_safe thing which
checks two features instead of one. The penalty we'd get is a single
inconditional JMP which in the face of XSAVE* is nothing.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--

  reply	other threads:[~2015-03-17  9:50 UTC|newest]

Thread overview: 126+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-04 18:30 Oops with tip/x86/fpu Dave Hansen
2015-03-04 19:06 ` Oleg Nesterov
2015-03-04 19:12   ` Dave Hansen
2015-03-04 20:06   ` Borislav Petkov
2015-03-05 15:14     ` Oleg Nesterov
     [not found]       ` <20150305182203.GA4203@redhat.com>
2015-03-05 18:34         ` Dave Hansen
2015-03-05 18:46           ` Oleg Nesterov
2015-03-05 18:41         ` Dave Hansen
2015-03-26 22:37         ` Yu, Fenghua
2015-03-26 22:43           ` Dave Hansen
2015-03-26 22:48             ` Yu, Fenghua
2015-03-27  7:30               ` Quentin Casasnovas
2015-03-27 19:06           ` Oleg Nesterov
2015-03-05  8:38   ` Quentin Casasnovas
2015-03-05 15:13     ` Oleg Nesterov
2015-03-05 18:42       ` Borislav Petkov
2015-03-05 22:16         ` Dave Hansen
2015-03-05 19:51 ` [PATCH 0/1] x86/fpu: math_state_restore() should not blindly disable irqs Oleg Nesterov
2015-03-05 19:51   ` [PATCH 1/1] " Oleg Nesterov
2015-03-05 20:11     ` Ingo Molnar
2015-03-05 21:25       ` Oleg Nesterov
2015-03-06  7:58         ` Ingo Molnar
2015-03-06 13:26           ` Oleg Nesterov
2015-03-06 13:39             ` Oleg Nesterov
2015-03-06 13:46             ` Ingo Molnar
2015-03-06 14:01               ` Oleg Nesterov
2015-03-06 14:17                 ` Oleg Nesterov
2015-03-06 15:00                 ` David Vrabel
2015-03-06 15:36                   ` Oleg Nesterov
2015-03-06 16:15                     ` David Vrabel
2015-03-06 16:31                       ` Oleg Nesterov
2015-03-06 17:33           ` Linus Torvalds
2015-03-06 18:15             ` Oleg Nesterov
2015-03-06 19:23             ` Andy Lutomirski
2015-03-06 22:00               ` Linus Torvalds
2015-03-06 22:28                 ` Andy Lutomirski
2015-03-07 10:36                   ` Ingo Molnar
2015-03-07 20:11                     ` Linus Torvalds
2015-03-08  8:55                       ` Ingo Molnar
2015-03-08 11:38                         ` Ingo Molnar
2015-03-08 13:59                         ` Andy Lutomirski
2015-03-08 14:38                           ` Andy Lutomirski
2015-03-07 10:32             ` Ingo Molnar
2015-03-07 15:38   ` [PATCH 0/1] x86/fpu: x86/fpu: avoid math_state_restore() without used_math() in __restore_xstate_sig() Oleg Nesterov
2015-03-07 15:38     ` [PATCH 1/1] " Oleg Nesterov
2015-03-09 14:07       ` Borislav Petkov
2015-03-09 14:34         ` Oleg Nesterov
2015-03-09 15:18           ` Borislav Petkov
2015-03-09 16:24             ` Oleg Nesterov
2015-03-09 16:53               ` Borislav Petkov
2015-03-09 17:05                 ` Oleg Nesterov
2015-03-09 17:23                   ` Borislav Petkov
2015-03-16 12:07       ` [tip:x86/urgent] x86/fpu: Avoid " tip-bot for Oleg Nesterov
2015-03-05 20:35 ` [PATCH 0/1] x86/fpu: math_state_restore() should not blindly disable irqs Oleg Nesterov
2015-03-09 17:10 ` [PATCH] x86/fpu: drop_fpu() should not assume that tsk == current Oleg Nesterov
2015-03-09 17:36   ` Rik van Riel
2015-03-09 17:48   ` Borislav Petkov
2015-03-09 18:06     ` Oleg Nesterov
2015-03-09 18:10       ` Borislav Petkov
2015-03-16 12:07   ` [tip:x86/urgent] x86/fpu: Drop_fpu() should not assume that tsk equals current tip-bot for Oleg Nesterov
2015-03-11 17:33 ` [PATCH 0/4] x86/fpu: avoid math_state_restore() on kthread exec Oleg Nesterov
2015-03-11 17:34   ` [PATCH 1/4] x86/fpu: document user_fpu_begin() Oleg Nesterov
2015-03-13  9:47     ` Borislav Petkov
2015-03-13 14:34       ` Oleg Nesterov
2015-03-23 12:20     ` [tip:x86/fpu] x86/fpu: Document user_fpu_begin() tip-bot for Oleg Nesterov
2015-03-11 17:34   ` [PATCH 2/4] x86/fpu: introduce restore_init_xstate() Oleg Nesterov
2015-03-13 10:34     ` Borislav Petkov
2015-03-13 14:39       ` Oleg Nesterov
2015-03-13 15:20         ` Borislav Petkov
2015-03-16 19:05           ` Rik van Riel
2015-03-23 12:20     ` [tip:x86/fpu] x86/fpu: Introduce restore_init_xstate() tip-bot for Oleg Nesterov
2015-03-11 17:34   ` [PATCH 3/4] x86/fpu: use restore_init_xstate() instead of math_state_restore() on kthread exec Oleg Nesterov
2015-03-13 10:48     ` Borislav Petkov
2015-03-13 14:45       ` Oleg Nesterov
2015-03-13 15:51         ` Borislav Petkov
2015-03-23 12:21     ` [tip:x86/fpu] x86/fpu: Use " tip-bot for Oleg Nesterov
2015-03-11 17:35   ` [PATCH 4/4] x86/fpu: don't abuse drop_init_fpu() in flush_thread() Oleg Nesterov
2015-03-13 10:52     ` Borislav Petkov
2015-03-13 14:55       ` Oleg Nesterov
2015-03-13 16:19         ` Borislav Petkov
2015-03-13 16:26           ` Oleg Nesterov
2015-03-13 19:27             ` Borislav Petkov
2015-03-14 14:48               ` Oleg Nesterov
2015-03-15 17:36                 ` Borislav Petkov
2015-03-15 18:16                   ` Oleg Nesterov
2015-03-15 18:50                     ` Borislav Petkov
2015-03-15 20:04                       ` Oleg Nesterov
2015-03-15 20:38                         ` Borislav Petkov
2015-03-16  9:35                           ` Borislav Petkov
2015-03-16 10:28                             ` Ingo Molnar
2015-03-16 14:39                             ` Oleg Nesterov
2015-03-16 15:26                               ` Borislav Petkov
2015-03-16 15:34                             ` Andy Lutomirski
2015-03-16 15:35                               ` Borislav Petkov
2015-03-13 17:30     ` [PATCH v2 " Oleg Nesterov
2015-03-14 10:55       ` Borislav Petkov
2015-03-14 10:57         ` [PATCH] x86/fpu: Fold __drop_fpu() into its sole user Borislav Petkov
2015-03-14 15:15           ` Oleg Nesterov
2015-03-16 10:27           ` Ingo Molnar
2015-03-23 12:21       ` [tip:x86/fpu] x86/fpu: Don't abuse drop_init_fpu() in flush_thread() tip-bot for Oleg Nesterov
2015-03-13 18:26 ` [PATCH 0/1] x86/cpu: don't allocate fpu->state for swapper/0 Oleg Nesterov
2015-03-13 18:27   ` [PATCH 1/1] " Oleg Nesterov
2015-03-16 10:18     ` Borislav Petkov
2015-03-23 12:22     ` [tip:x86/fpu] x86/fpu: Don't " tip-bot for Oleg Nesterov
2015-03-14 11:16   ` [PATCH 0/1] x86/cpu: don't " Borislav Petkov
2015-03-14 15:13     ` [PATCH 0/1] x86/cpu: kill eager_fpu_init_bp() Oleg Nesterov
2015-03-14 15:13       ` [PATCH 1/1] " Oleg Nesterov
2015-03-16 12:44         ` Borislav Petkov
2015-03-23 12:22         ` [tip:x86/fpu] x86/fpu: Kill eager_fpu_init_bp() tip-bot for Oleg Nesterov
2015-03-15 16:49 ` [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in xsave_user/xrestore_user Oleg Nesterov
2015-03-15 16:50   ` [PATCH RFC 1/2] x86: introduce __user_insn() and __check_insn() Oleg Nesterov
2015-03-15 16:50   ` [PATCH RFC 2/2] x86/fpu: change xsave_user() and xrestore_user() to use __user_insn() Oleg Nesterov
2015-03-16 22:43     ` Quentin Casasnovas
2015-03-17  9:35       ` Borislav Petkov
2015-03-16 14:36   ` [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in xsave_user/xrestore_user Borislav Petkov
2015-03-16 14:57     ` Oleg Nesterov
2015-03-16 17:58       ` Borislav Petkov
2015-03-16 22:37   ` Quentin Casasnovas
2015-03-17  9:47     ` Borislav Petkov [this message]
2015-03-17 10:00       ` Quentin Casasnovas
2015-03-17 11:20         ` Borislav Petkov
2015-03-17 11:36           ` Quentin Casasnovas
2015-03-17 12:07             ` Borislav Petkov
2015-03-18  9:06               ` Quentin Casasnovas
2015-03-18  9:53                 ` Borislav Petkov
2015-03-17 10:07       ` Quentin Casasnovas

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