linux-kernel - Re: x86: Disable SSE4A

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Message-ID: <5deb806b-4bd0-47c9-a8ba-868cd4c9dfd4@amd.com>
Date: Tue, 28 Oct 2025 09:32:02 +0100
From: Christian König <christian.koenig@....com>
To: Arisu Tachibana <arisu.tachibana@...aclelinux.com>,
 Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>, x86@...nel.org,
 Leyvi Rose <leyvirose@...il.com>, Samuel Holland
 <samuel.holland@...ive.com>, Masami Hiramatsu <mhiramat@...nel.org>,
 lkml <linux-kernel@...r.kernel.org>, "Wentland, Harry"
 <Harry.Wentland@....com>, "Li, Sun peng (Leo)" <Sunpeng.Li@....com>,
 Rodrigo Siqueira <siqueira@...lia.com>
Subject: Re: x86: Disable SSE4A

Adding AMDs DC people (the component which enables FPU in amdgpu) on CC.

On 10/28/25 05:19, Arisu Tachibana wrote:
> On Mon, Oct 27, 2025 at 9:41 PM Borislav Petkov <bp@...en8.de> wrote:
>>
>> On Mon, Oct 27, 2025 at 12:40:59PM +0100, Peter Zijlstra wrote:
>>> Leyvi Rose reported that his X86_NATIVE_CPU=y build is failing because
>>> our instruction decoder doesn't support SSE4A and the AMDGPU code seems
>>> to be generating those with his compiler of choice (CLANG+LTO).
>>>
>>> Now, our normal build flags disable SSE MMX SSE2 3DNOW AVX, but then
>>> CC_FLAGS_FPU re-enable SSE SSE2.
>>>
>>> Since nothing mentions SSE3 or SSE4, I'm assuming that -msse (or its
>>> negative) control all SSE variants -- but why then explicitly enumerate
>>> SSE2 ?
>>>
>>> Anyway, until the instruction decoder gets fixed, explicitly disallow
>>> SSE4A (an AMD specific SSE4 extension).
>>>
>>> Fixes: ea1dcca1de12 ("x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU option to locally optimize the kernel with '-march=native'")
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>>> ---
>>>
>>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
>>> index 4db7e4bf69f5..8fbff3106c56 100644
>>> --- a/arch/x86/Makefile
>>> +++ b/arch/x86/Makefile
>>> @@ -75,7 +75,7 @@ export BITS
>>>  #
>>>  #    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
>>>  #
>>> -KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
>>> +KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -mno-sse4a
>>>  KBUILD_RUSTFLAGS += --target=$(objtree)/scripts/target.json
>>>  KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
>>
>> Acked-by: Borislav Petkov (AMD) <bp@...en8.de>
>>
> 
>  Acked-by: Arisu Tachibana <arisu.tachibana@...aclelinux.com>

Acked-by: Christian König <christian.koenig@....com>

> 
> 
> --
> thanks,
> arisut