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From: Tom Lendacky <thomas.lendacky@amd.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	David Woodhouse <dwmw@amazon.co.uk>, Paul Turner <pjt@google.com>,
	Andrew Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Greg Kroah-Hartman <gregkh@linux-foundation.org>,
	Dave Hansen <dave.hansen@intel.com>,
	Jiri Kosina <jikos@kernel.org>, Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH] x86/retpoline: Fix NOSPEC_JMP for tip
Date: Tue, 9 Jan 2018 18:45:34 -0600	[thread overview]
Message-ID: <184a65a3-6afe-4c82-7f7d-2c1d4a5198bc@amd.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1801100139560.2200@nanos>

On 1/9/2018 6:40 PM, Thomas Gleixner wrote:
> On Tue, 9 Jan 2018, Linus Torvalds wrote:
> 
>> On Tue, Jan 9, 2018 at 4:31 PM, Andi Kleen <andi@firstfloor.org> wrote:
>>>
>>> The following patch fixes it for me. Something doesn't
>>> seem to work with ALTERNATIVE_2. It adds only a few bytes
>>> more code, so seems acceptable.
>>
>> Ugh. It's kind of stupid, though.
>>
>> Why is the code sequence not simply:
>>
>>   ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE_AMD
>>   ALTERNATIVE __stringify(jmp *\reg), __stringify(RETPOLINE_JMP \reg),
>> X86_FEATURE_RETPOLINE
>>
>> ie make that X86_FEATURE_RETPOLINE_AMD _only_ emit the "lfence", and
>> simply fall through to what will be the "jmp *\reg" of the
>> non-RETPOLINE version.
>>
>> Then just make sure X86_FEATURE_RETPOLINE_AMD disables X86_FEATURE_RETPOLINE.

I think there are areas that rely on X86_FEATURE_RETPOLINE being set
even if X86_FEATURE_RETPOLINE_AMD is set.  For example, line 261 in
arch/x86/entry/entry_32.S is only checking for X86_FEATURE_RETPOLINE.

Thanks,
Tom

>>
>> That is both simpler an dsmaller, no?
> 
> Duh, yes.
> 

  reply	other threads:[~2018-01-10  0:45 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-10  0:31 [PATCH] x86/retpoline: Fix NOSPEC_JMP for tip Andi Kleen
2018-01-10  0:39 ` Thomas Gleixner
2018-01-10  0:39 ` Linus Torvalds
2018-01-10  0:40   ` Thomas Gleixner
2018-01-10  0:45     ` Tom Lendacky [this message]
2018-01-10  0:50       ` Thomas Gleixner
2018-01-10  1:30       ` Andi Kleen
2018-01-10  1:36         ` Andi Kleen
2018-01-10  1:50           ` Thomas Gleixner
2018-01-10  1:57             ` Andi Kleen
2018-01-10  9:05         ` David Woodhouse
2018-01-10  0:51   ` Andi Kleen
2018-01-10  1:05     ` Thomas Gleixner
2018-01-10  7:15   ` David Woodhouse
2018-01-10 10:05     ` David Woodhouse
2018-01-10 11:28       ` [PATCH] x86/alternatives: Fix optimize_nops() checking Borislav Petkov
2018-01-10 11:36         ` David Woodhouse
2018-01-10 11:45           ` Borislav Petkov
2018-01-10 11:49             ` David Woodhouse
2018-01-10 11:57               ` Borislav Petkov
2018-01-10 11:58                 ` David Woodhouse
2018-01-10 17:33         ` [tip:x86/pti] " tip-bot for Borislav Petkov
2018-01-10 18:12         ` tip-bot for Borislav Petkov
2018-01-10 18:39         ` tip-bot for Borislav Petkov
2018-01-10 19:38         ` [PATCH] " Linus Torvalds
2018-01-10 19:55           ` Thomas Gleixner
2018-01-10 20:15             ` Josh Poimboeuf
2018-01-10 20:19               ` David Woodhouse
2018-01-10 20:26               ` Linus Torvalds
2018-01-10 20:33                 ` Peter Zijlstra
2018-01-10 20:36                   ` David Woodhouse
2018-01-10 20:49                   ` Linus Torvalds
2018-01-10 20:55                 ` Borislav Petkov
2018-01-10 21:05                   ` Linus Torvalds
2018-01-10 21:08                     ` David Woodhouse
2018-01-10 21:11                       ` Linus Torvalds
2018-01-10 21:16                         ` Josh Poimboeuf
2018-01-10 21:17                         ` Linus Torvalds
2018-01-10 21:27                           ` Josh Poimboeuf
2018-01-10 21:10                     ` Borislav Petkov
2018-01-10 20:55                 ` Josh Poimboeuf
2018-01-10 20:05           ` Borislav Petkov
2018-01-10 20:20             ` Linus Torvalds
2018-01-10 20:50               ` Borislav Petkov

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