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From: Andy Lutomirski <luto@amacapital.net>
To: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>, Peter Anvin <hpa@zytor.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Brian Gerst <brgerst@gmail.com>,
	Matthew Whitehead <tedheadster@gmail.com>,
	Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH] x86/alternatives: Do not use sync_core() to serialize I$
Date: Sat, 3 Dec 2016 09:05:39 -0800	[thread overview]
Message-ID: <CALCETrXzdAUVV76KDJUKyk-3CMFoUteMYCHTjB+mXZeFzRoGog@mail.gmail.com> (raw)
In-Reply-To: <20161203150258.vwr5zzco7ctgc4pe@pd.tnic>

On Sat, Dec 3, 2016 at 7:02 AM, Borislav Petkov <bp@alien8.de> wrote:
> On Fri, Dec 02, 2016 at 08:28:44PM +0100, Borislav Petkov wrote:
>> Ah, it is called only from apply_alternatives() but sure, it is safer
>> this way. Lemme do that and run it through the boxes to see whether
>> anything catches fire.
>
> Looks good, ran it on a bunch of machines, two of them huge AMD and
> Intel, 8-socket monsters.
>
> Here is a version with a commit message:
>
> ---
> From: Borislav Petkov <bp@suse.de>
> Date: Fri, 2 Dec 2016 23:18:51 +0100
> Subject: [PATCH] x86/alternatives: Do not use sync_core() to serialize I$
>
> We use sync_core() in the alternatives code to stop speculative
> execution of prefetched instructions because we are potentially changing
> them and don't want to execute stale bytes.
>
> What it does on most machines is call CPUID which is a serializing
> instruction. And that's expensive.
>
> However, the instruction cache is serialized when we're on the local CPU
> and are changing the data through the same virtual address. So then, we
> don't need the serializing CPUID but a simple control flow change. Last
> being accomplished with a CALL/RET which the noinline causes.
>
> So let's try it.

I like it.

Reviewed-by: Andy Lutomirski <luto@kernel.org>

  reply	other threads:[~2016-12-03 17:13 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-30 20:34 [PATCH 0/4] CPUID-less CPU fixes and improvements Andy Lutomirski
2016-11-30 20:34 ` [PATCH 1/4] x86/asm/32: Make sync_core() handle missing CPUID on all 32-bit kernels Andy Lutomirski
2016-11-30 20:34 ` [PATCH 2/4] Revert "x86/boot: Fail the boot if !M486 and CPUID is missing" Andy Lutomirski
2016-12-01  5:53   ` Peter Zijlstra
2016-12-01  9:02     ` Borislav Petkov
2016-12-01 10:07       ` Thomas Gleixner
2016-12-01 11:15         ` [PATCH] x86/CPU: Add X86_FEATURE_CPUID Borislav Petkov
2016-12-01 17:00           ` Andy Lutomirski
2016-12-02  0:33       ` [PATCH 2/4] Revert "x86/boot: Fail the boot if !M486 and CPUID is missing" Andy Lutomirski
2016-12-01 17:00     ` Andy Lutomirski
2016-11-30 20:34 ` [PATCH 3/4] x86/microcode/intel: Replace sync_core() with cpuid_eax(1) Andy Lutomirski
2016-12-01  9:11   ` Borislav Petkov
2016-11-30 20:34 ` [PATCH 4/4] x86/asm: Change sync_core() to use MOV to CR2 to serialize Andy Lutomirski
2016-12-01  9:22   ` Borislav Petkov
2016-12-01 17:08     ` Andy Lutomirski
2016-12-01 17:46       ` Andrew Cooper
2016-12-02  7:34     ` Ingo Molnar
2016-12-02  0:34 ` [PATCH v2 0/6] CPUID-less CPU/sync_core fixes and improvements Andy Lutomirski
2016-12-02  0:34   ` [PATCH v2 1/6] x86/asm/32: Make sync_core() handle missing CPUID on all 32-bit kernels Andy Lutomirski
2016-12-02  0:34   ` [PATCH v2 2/6] Revert "x86/boot: Fail the boot if !M486 and CPUID is missing" Andy Lutomirski
2016-12-02  0:34   ` [PATCH v2 3/6] x86/microcode/intel: Replace sync_core() with cpuid_eax(1) Andy Lutomirski
2016-12-02  0:35   ` [PATCH v2 4/6] x86/paravirt: Make sync_core() be a paravirt op Andy Lutomirski
2016-12-02  0:35   ` [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski
2016-12-02 11:44     ` Andrew Cooper
2016-12-02 11:44     ` Andrew Cooper
2016-12-02 17:07       ` Andy Lutomirski
2016-12-02 17:07       ` Andy Lutomirski
2016-12-02 17:16         ` Andrew Cooper
2016-12-02 17:16         ` Andrew Cooper
2016-12-02 17:23           ` Andy Lutomirski
2016-12-02 17:26             ` Andrew Cooper
2016-12-02 17:26             ` Andrew Cooper
2016-12-02 17:23           ` Andy Lutomirski
2016-12-02 18:50       ` Boris Ostrovsky
2016-12-02 18:50       ` Boris Ostrovsky
2016-12-02 19:34         ` Andy Lutomirski
2016-12-02 19:34         ` Andy Lutomirski
2016-12-02 20:09       ` Boris Ostrovsky
2016-12-02 20:09         ` Boris Ostrovsky
2016-12-02 17:32     ` Linus Torvalds
2016-12-02 17:38       ` Andy Lutomirski
2016-12-02 17:53         ` Linus Torvalds
2016-12-02 18:03         ` Borislav Petkov
2016-12-02 18:27           ` Linus Torvalds
2016-12-02 18:50             ` Borislav Petkov
2016-12-02 19:03               ` Linus Torvalds
2016-12-02 19:20                 ` Borislav Petkov
2016-12-02 19:24                   ` Linus Torvalds
2016-12-02 19:28                     ` Borislav Petkov
2016-12-03 15:02                       ` [PATCH] x86/alternatives: Do not use sync_core() to serialize I$ Borislav Petkov
2016-12-03 17:05                         ` Andy Lutomirski [this message]
2016-12-20  7:58                         ` [tip:x86/urgent] " tip-bot for Borislav Petkov
2016-12-20  9:35                         ` tip-bot for Borislav Petkov
2016-12-02 19:30                     ` [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation Andy Lutomirski
2016-12-02 19:35                       ` Linus Torvalds
2016-12-02 20:41                         ` Andy Lutomirski
2016-12-02 21:10                           ` Linus Torvalds
2016-12-02 22:55                             ` Andy Lutomirski
2016-12-02 23:09                               ` Linus Torvalds
2016-12-02 19:23                 ` Andy Lutomirski
2016-12-02 19:30                   ` Borislav Petkov
2016-12-03 12:44         ` Borislav Petkov
2016-12-02  0:35   ` [PATCH v2 6/6] x86/asm: Change sync_core() to use MOV to CR2 to serialize Andy Lutomirski
2016-12-02  0:36 ` [PATCH 0/4] CPUID-less CPU fixes and improvements Andy Lutomirski
2016-12-02 10:17   ` Ingo Molnar

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