Received-SPF: pass (google.com: domain of linux-kernel+bounces-14264-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Message-ID: <7a6aa1bbdbbe2e63ae96ff163fab0349f58f1b9e.camel@xry111.site>
Subject: MIPS: fcsr31 may be dirty after execve when kernel preempt is
 enabled (was: Re: [PATCH v2] LoongArch: Fix and simplify fcsr
 initialization on execve)
From: Xi Ruoyao <xry111@xry111.site>
To: Huacai Chen <chenhuacai@kernel.org>, WANG Xuerui <kernel@xen0n.name>, 
	Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Eric Biederman <ebiederm@xmission.com>, Kees Cook
 <keescook@chromium.org>,  Tiezhu Yang <yangtiezhu@loongson.cn>, Jinyang He
 <hejinyang@loongson.cn>, loongarch@lists.linux.dev,  linux-mm@kvack.org,
 linux-kernel@vger.kernel.org, stable@vger.kernel.org, 
 linux-mips@vger.kernel.org
Date: Tue, 02 Jan 2024 18:48:27 +0800
In-Reply-To: <f6e0b3a0e08a8100fa5dc9345af8582ff664321c.camel@xry111.site>
References: <20240102101711.10872-2-xry111@xry111.site>
	 <f6e0b3a0e08a8100fa5dc9345af8582ff664321c.camel@xry111.site>
Autocrypt: addr=xry111@xry111.site; prefer-encrypt=mutual;
 keydata=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
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.50.2 
Precedence: bulk
MIME-Version: 1.0

On Tue, 2024-01-02 at 18:25 +0800, Xi Ruoyao wrote:
> On Tue, 2024-01-02 at 18:17 +0800, Xi Ruoyao wrote:
> > The only other architecture setting FCSR in SET_PERSONALITY2 is MIPS.
> > They do this for supporting different FP flavors (NaN encodings etc).
> > which do not exist on LoongArch.=C2=A0 I'm not sure how MIPS evades the=
 issue
> > (or maybe it's just buggy too) but I'll investigate it later.
>=20
> Phew.=C2=A0 I just managed to recommission my 3A4000 and I can reproduce =
the
> issue as well with Linux 5.18.1 (the latest kernel release when I
> decommissioned it) and CONFIG_PREEMPT=3Dy.
>=20
> % cat measure.c
> #include <fenv.h>
> int main() { return fetestexcept(FE_INEXACT); }
>=20
> % echo $((1./3))
> 0.33333333333333331
>=20
> % while ./a.out; do ; done
> (stopped in seconds)
>=20
> I'm building the mainline kernel on the 3A4000 now, will see if the
> issue still exists...

Still happening with 6.7.0-rc8.  I'm not sure how to fix it for MIPS.=20
Maybe lose_fpu in SET_PERSONALITY2? But to me doing so will be really
nasty.  Anyway I'll leave this for MIPS maintainers.

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University