From: Brian Gerst <brgerst@gmail.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>,
"the arch/x86 maintainers" <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Denys Vlasenko <dvlasenk@redhat.com>,
Andy Lutomirski <luto@amacapital.net>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init
Date: Tue, 19 Jan 2016 23:39:43 -0500 [thread overview]
Message-ID: <CAMzpN2hz4wUFf6Uc6TFovXmT6F-t8kbc9VQd_E=-p+K-TJaK2A@mail.gmail.com> (raw)
In-Reply-To: <569F06B9.4060903@zytor.com>
On Tue, Jan 19, 2016 at 11:02 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 01/19/16 01:22, Borislav Petkov wrote:
>> On Mon, Jan 18, 2016 at 05:33:03PM -0800, H. Peter Anvin wrote:
>>> Why the f do we call a subroutine for what amounts to a single bt or
>>> test instruction?
>>
>> No real reason. You can kick me when you see me next time:
>>
>> 4a90a99c4f80 ("x86: Add a static_cpu_has_safe variant")
>>
>
> So, here is my suggestion:
>
> 1. Just get rid of static_cpu_has_safe() and make static_cpu_has() safe.
>
> 2. Get rid of the non-asm goto variant and just fall back to dynamic if
> asm goto is unavailable. It doesn't make any sense, really, if it is
> supposed to be safe, and by now the asm goto-capable gcc is in more wide
> use. (Originally the gcc 3.x fallback to pure dynamic didn't exist,
> either.)
>
> 3. Put the dynamic test in the .init.text section and inline it:
>
> .section .init.text,"ax"
> testb %2,%3
> jnz %[t_yes]
> jmp %[t_no]
> .previous
>
> ... "i" (1 << (bit & 7)),
> "m" (((const char *)boot_cpu_data->x86_capability)[bit >> 3]) ...
Can't put it in .init.text or else you get:
WARNING: arch/x86/kernel/built-in.o(.text+0x4b9): Section mismatch in
reference from the function __switch_to() to the (unknown reference)
.init.text:(unknown)
The function __switch_to() references
the (unknown reference) __init (unknown).
This is often because __switch_to lacks a __init
annotation or the annotation of (unknown) is wrong.
We want to override that because we know that the reference will be
removed after alternatives run. That's why I created a new section.
--
Brian Gerst
next prev parent reply other threads:[~2016-01-20 4:39 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-16 19:22 [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Brian Gerst
2016-01-16 19:36 ` Borislav Petkov
2016-01-16 19:58 ` Brian Gerst
2016-01-17 10:33 ` Borislav Petkov
2016-01-18 16:52 ` Brian Gerst
2016-01-18 17:49 ` Andy Lutomirski
2016-01-18 18:14 ` Borislav Petkov
2016-01-18 18:29 ` Andy Lutomirski
2016-01-18 18:39 ` Borislav Petkov
2016-01-18 19:45 ` H. Peter Anvin
2016-01-18 23:05 ` Borislav Petkov
2016-01-18 23:13 ` H. Peter Anvin
2016-01-18 23:25 ` Borislav Petkov
2016-01-19 13:57 ` Borislav Petkov
2016-01-19 16:23 ` Borislav Petkov
2016-01-19 23:10 ` Borislav Petkov
2016-01-19 23:26 ` Andy Lutomirski
2016-01-19 23:49 ` Boris Petkov
2016-01-20 4:03 ` H. Peter Anvin
2016-01-20 10:33 ` Borislav Petkov
2016-01-20 10:41 ` H. Peter Anvin
2016-01-21 22:14 ` Borislav Petkov
2016-01-21 22:22 ` H. Peter Anvin
2016-01-21 22:56 ` Borislav Petkov
2016-01-21 23:36 ` H. Peter Anvin
2016-01-21 23:37 ` H. Peter Anvin
2016-01-22 10:32 ` Borislav Petkov
2016-01-18 18:51 ` Borislav Petkov
2016-01-19 1:10 ` Borislav Petkov
2016-01-19 1:33 ` H. Peter Anvin
2016-01-19 9:22 ` Borislav Petkov
2016-01-20 4:02 ` H. Peter Anvin
2016-01-20 4:39 ` Brian Gerst [this message]
2016-01-20 4:42 ` H. Peter Anvin
2016-01-20 10:50 ` Borislav Petkov
2016-01-20 10:55 ` H. Peter Anvin
2016-01-20 11:05 ` Borislav Petkov
2016-01-20 14:48 ` H. Peter Anvin
2016-01-20 15:01 ` Borislav Petkov
2016-01-20 15:09 ` H. Peter Anvin
2016-01-20 16:04 ` Borislav Petkov
2016-01-20 16:16 ` H. Peter Anvin
2016-01-23 6:50 [PATCH] x86/head_64.S: do not use temporary register to check alignment Alexander Kuleshov
2016-01-26 9:31 ` Borislav Petkov
2016-01-26 21:12 [PATCH 00/10] tip-queue 2016-01-26, rest Borislav Petkov
2016-01-26 21:12 ` [PATCH 01/10] x86/asm: Add condition codes clobber to memory barrier macros Borislav Petkov
2016-01-26 21:12 ` [PATCH 02/10] x86/asm: Drop a comment left over from X86_OOSTORE Borislav Petkov
2016-01-26 21:12 ` [PATCH 03/10] x86/asm: Tweak the comment about wmb() use for IO Borislav Petkov
2016-01-26 21:12 ` [PATCH 04/10] x86/cpufeature: Carve out X86_FEATURE_* Borislav Petkov
2016-01-30 13:18 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-26 21:12 ` [PATCH 05/10] x86/cpufeature: Replace the old static_cpu_has() with safe variant Borislav Petkov
2016-01-30 13:19 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-26 21:12 ` [PATCH 06/10] x86/cpufeature: Get rid of the non-asm goto variant Borislav Petkov
2016-01-27 3:36 ` Brian Gerst
2016-01-27 8:41 ` Borislav Petkov
2016-01-27 8:43 ` [PATCH -v1.1 " Borislav Petkov
2016-01-30 13:19 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-27 8:45 ` [PATCH -v1.1 8/10] x86/alternatives: Discard dynamic check after init Borislav Petkov
2016-01-30 13:20 ` [tip:x86/asm] " tip-bot for Brian Gerst
2016-01-26 21:12 ` [PATCH 07/10] x86/alternatives: Add an auxilary section Borislav Petkov
2016-01-30 13:19 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-26 21:12 ` [PATCH 08/10] x86/alternatives: Discard dynamic check after init Borislav Petkov
2016-01-26 21:12 ` [PATCH 09/10] x86/vdso: Use static_cpu_has() Borislav Petkov
2016-01-30 13:20 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-26 21:12 ` [PATCH 10/10] x86/head_64: Simplify kernel load address alignment check Borislav Petkov
2016-01-30 13:20 ` [tip:x86/boot] x86/boot: " tip-bot for Alexander Kuleshov
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