From: Andi Kleen <andi@firstfloor.org>
To: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
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 17:30:09 -0800 [thread overview]
Message-ID: <20180110013009.5ysxlkuhczuv7uwg@two.firstfloor.org> (raw)
In-Reply-To: <184a65a3-6afe-4c82-7f7d-2c1d4a5198bc@amd.com>
On Tue, Jan 09, 2018 at 06:45:34PM -0600, Tom Lendacky wrote:
> 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.
I audited the difference places. They all seem ok.
I assume you don't need FILL_RETURN_BUFFER on AMD. If not let me know
and we can add a X86_FEATURE_RETPOLINE_COMMON
-Andi
next prev parent reply other threads:[~2018-01-10 1:30 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
2018-01-10 0:50 ` Thomas Gleixner
2018-01-10 1:30 ` Andi Kleen [this message]
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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