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From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: X86 ML <x86@kernel.org>, Andy Lutomirski <luto@amacapital.net>,
	LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2 07/15] x86/lib/copy_user_64.S: Convert to ALTERNATIVE_2
Date: Wed, 4 Mar 2015 08:13:24 +0100	[thread overview]
Message-ID: <20150304071324.GA22028@gmail.com> (raw)
In-Reply-To: <20150304062552.GA16111@gmail.com>


* Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Borislav Petkov <bp@alien8.de> wrote:
> 
> > From: Borislav Petkov <bp@suse.de>
> > 
> > Use the asm macro and drop the locally grown version.
> 
> > @@ -73,9 +49,11 @@ ENTRY(_copy_to_user)
> >  	jc bad_to_user
> >  	cmpq TI_addr_limit(%rax),%rcx
> >  	ja bad_to_user
> > +	ALTERNATIVE_2 "jmp copy_user_generic_unrolled",		\
> > +		      "jmp copy_user_generic_string",		\
> > +		      X86_FEATURE_REP_GOOD,			\
> > +		      "jmp copy_user_enhanced_fast_string",	\
> > +		      X86_FEATURE_ERMS
> 
> Btw., as a future optimization, wouldn't it be useful to patch this 
> function at its first instruction, i.e. to have three fully functional 
> copy_user_generic_ variants and choose to jmp to one of them in the 
> first instruction of the original function?
> 
> The advantage would be two-fold:
> 
>  1) right now: smart microarchitectures that are able to optimize
>     jump-after-jump (and jump-after-call) targets in their branch
>     target cache can do so in this case, reducing the overhead of the
>     patching, possibly close to zero in the cached case.

Btw., the x86 memset() variants are using this today, and I think this 
is the most optimal jump-patching variant, even if it means a small 
amount of code duplication between the copy_user variants.

Thanks,

	Ingo

  reply	other threads:[~2015-03-04  7:13 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-24 11:14 [PATCH v2 00/15] x86, alternatives: Instruction padding and more robust JMPs Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 01/15] x86/lib/copy_user_64.S: Remove FIX_ALIGNMENT define Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 02/15] x86/alternatives: Cleanup DPRINTK macro Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 03/15] x86/alternatives: Add instruction padding Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 04/15] x86/alternatives: Make JMPs more robust Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 05/15] x86/alternatives: Use optimized NOPs for padding Borislav Petkov
2015-03-04  6:43   ` Ingo Molnar
2015-03-04  8:42     ` Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 06/15] x86/lib/copy_page_64.S: Use generic ALTERNATIVE macro Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 07/15] x86/lib/copy_user_64.S: Convert to ALTERNATIVE_2 Borislav Petkov
2015-03-04  6:25   ` Ingo Molnar
2015-03-04  7:13     ` Ingo Molnar [this message]
2015-03-04  9:06       ` Borislav Petkov
2015-03-05  0:34         ` Ingo Molnar
2015-03-05  8:23           ` Borislav Petkov
2015-03-04  9:00     ` Borislav Petkov
2015-03-05  0:32       ` Ingo Molnar
2015-03-05  8:35         ` Borislav Petkov
2015-03-05  9:34           ` Ingo Molnar
2015-03-05  9:46             ` Ingo Molnar
2015-02-24 11:14 ` [PATCH v2 08/15] x86/smap: Use ALTERNATIVE macro Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 09/15] x86/entry_32: Convert X86_INVD_BUG to " Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 10/15] x86/lib/clear_page_64.S: Convert to ALTERNATIVE_2 macro Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 11/15] x86/asm: Use alternative_2() in rdtsc_barrier() Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 12/15] x86/asm: Cleanup prefetch primitives Borislav Petkov
2015-03-04  6:48   ` Ingo Molnar
2015-03-04  9:08     ` Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 13/15] x86/lib/memset_64.S: Convert to ALTERNATIVE_2 macro Borislav Petkov
2015-02-24 11:14 ` [PATCH v2 14/15] x86/lib/memmove_64.S: Convert memmove() to ALTERNATIVE macro Borislav Petkov
2015-03-04  7:19   ` Ingo Molnar
2015-02-24 11:14 ` [PATCH v2 15/15] x86/lib/memcpy_64.S: Convert memcpy to ALTERNATIVE_2 macro Borislav Petkov
2015-03-04  7:26   ` Ingo Molnar
2015-03-04 13:58     ` Borislav Petkov
2015-03-05  0:26       ` Ingo Molnar
2015-03-05  8:37         ` Borislav Petkov
2015-02-24 20:25 ` [PATCH v2 00/15] x86, alternatives: Instruction padding and more robust JMPs Andy Lutomirski
2015-02-26 18:13 ` Borislav Petkov
2015-02-26 18:16   ` [PATCH 1/3] perf/bench: Fix mem* routines usage after alternatives change Borislav Petkov
2015-02-26 18:16     ` [PATCH 2/3] perf/bench: Carve out mem routine benchmarking Borislav Petkov
2015-02-26 18:16     ` [PATCH 3/3] perf/bench: Add -r all so that you can run all mem* routines Borislav Petkov
2015-03-04  7:30       ` Ingo Molnar
2015-03-02 14:51   ` [PATCH v2 00/15] x86, alternatives: Instruction padding and more robust JMPs Hitoshi Mitake
2015-03-02 16:27     ` Borislav Petkov

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