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From: "H. Peter Anvin" <hpa@zytor.com>
To: Borislav Petkov <bp@alien8.de>
Cc: X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
	Borislav Petkov <bp@suse.de>
Subject: Re: [PATCH 2/3] x86: Sanity-check static_cpu_has usage
Date: Mon, 29 Apr 2013 08:38:45 -0700	[thread overview]
Message-ID: <517E9405.8030509@zytor.com> (raw)
In-Reply-To: <1367244262-29511-3-git-send-email-bp@alien8.de>

On 04/29/2013 07:04 AM, Borislav Petkov wrote:
> From: Borislav Petkov <bp@suse.de>
> 
> static_cpu_has may be used only after alternatives have run. Before that
> it always returns false if constant folding with __builtin_constant_p()
> doesn't happen. And you don't want that.
> 
> This patch is the result of me debugging an issue where I overzealously
> put static_cpu_has in code which executed before alternatives have run
> and had to spend some time with scratching head and cursing at the
> monitor.
> 
> So add a jump to a warning which screams loudly when we use this
> function too early. The alternatives patch that check away in
> conjunction with patching the rest of the kernel image.
> 
> This first JMP the compiler then issues should always be a two-byte JMP
> because its relative offset fits in a byte. This gets replaced by only a
> two-byte NOP => less instruction cache bloat.
> 

I still would prefer this to be an option.

	-hpa



  reply	other threads:[~2013-04-29 15:39 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-29 14:04 [PATCH 0/3] FPU detection in C, second try Borislav Petkov
2013-04-29 14:04 ` [PATCH 1/3] x86: Get rid of ->hard_math and all the FPU asm fu Borislav Petkov
2013-04-29 14:04 ` [PATCH 2/3] x86: Sanity-check static_cpu_has usage Borislav Petkov
2013-04-29 15:38   ` H. Peter Anvin [this message]
2013-04-29 14:04 ` [PATCH 3/3] x86, FPU: Do not use static_cpu_has before alternatives Borislav Petkov
2013-04-29 15:42   ` H. Peter Anvin
2013-04-29 18:51     ` Borislav Petkov
2013-04-29 18:58       ` H. Peter Anvin
  -- strict thread matches above, loose matches on Subject: below --
2013-04-08 15:57 [PATCH 0/4] x86: FPU detection in C Borislav Petkov
2013-04-08 15:57 ` [PATCH 1/4] x86: Get rid of ->hard_math and all the FPU asm fu Borislav Petkov
2013-04-08 16:26   ` [tip:x86/cpu] " tip-bot for H. Peter Anvin
2013-06-12 20:48   ` [tip:x86/fpu] " tip-bot for H. Peter Anvin
2013-04-08 15:57 ` [PATCH 2/4] x86: Fold-in trivial check_config function Borislav Petkov
2013-04-08 16:27   ` [tip:x86/cpu] " tip-bot for Borislav Petkov
2013-04-16 13:51   ` tip-bot for Borislav Petkov
2013-04-08 15:57 ` [PATCH 3/4] x86, AMD: Correct {rd,wr}msr_amd_safe warnings Borislav Petkov
2013-04-08 16:28   ` [tip:x86/cpu] " tip-bot for Borislav Petkov
2013-04-16 13:53   ` tip-bot for Borislav Petkov
2013-04-08 15:57 ` [PATCH 4/4] x86, CPU, AMD: Drop useless label Borislav Petkov
2013-04-08 16:29   ` [tip:x86/cpu] " tip-bot for Borislav Petkov
2013-04-16 13:54   ` tip-bot for Borislav Petkov
2013-04-10 11:08 ` [PATCH 0/4] x86: FPU detection in C Ingo Molnar
2013-04-10 12:24   ` Borislav Petkov
2013-04-10 12:25     ` Ingo Molnar
2013-04-10 13:32       ` Borislav Petkov
2013-04-10 15:35         ` H. Peter Anvin
2013-04-10 16:11           ` Borislav Petkov
2013-04-10 21:29             ` [PATCH] x86, FPU: Fix FPU initialization Borislav Petkov
2013-04-11 12:09               ` Ingo Molnar
2013-04-11 14:23                 ` Borislav Petkov
2013-04-11 19:26                 ` H. Peter Anvin
2013-04-11 20:23                   ` Borislav Petkov
2013-04-12  5:32                     ` Ingo Molnar
2013-04-12  5:34                       ` H. Peter Anvin
2013-04-12  9:47                         ` Borislav Petkov
2013-04-12 11:26                           ` Borislav Petkov
2013-04-15 10:08                             ` Ingo Molnar
2013-04-15 10:17                               ` Borislav Petkov
2013-04-15 10:18                                 ` Ingo Molnar
2013-04-15 15:54                                   ` Borislav Petkov
2013-04-15 22:04                                     ` Borislav Petkov
2013-04-16  9:25                                       ` Ingo Molnar
2013-04-16  9:48                                         ` Borislav Petkov
2013-04-16 10:08                                           ` [GIT PULL] Rebase tip:x86/cpu Borislav Petkov
2013-04-16 11:35                                             ` Ingo Molnar
2013-04-16 11:33                                           ` [PATCH] x86, FPU: Fix FPU initialization Ingo Molnar

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