Received-SPF: pass (google.com: domain of linux-kernel+bounces-14283-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Precedence: bulk
MIME-Version: 1.0
References: <20240102101711.10872-2-xry111@xry111.site> <f6e0b3a0e08a8100fa5dc9345af8582ff664321c.camel@xry111.site>
 <7a6aa1bbdbbe2e63ae96ff163fab0349f58f1b9e.camel@xry111.site>
In-Reply-To: <7a6aa1bbdbbe2e63ae96ff163fab0349f58f1b9e.camel@xry111.site>
From: Huacai Chen <chenhuacai@kernel.org>
Date: Tue, 2 Jan 2024 19:20:57 +0800
Message-ID: <CAAhV-H7oMB62mSL1O4QPdUNW5z1_12G3L5QAm81KsSwDv_GsEg@mail.gmail.com>
Subject: Re: MIPS: fcsr31 may be dirty after execve when kernel preempt is
 enabled (was: Re: [PATCH v2] LoongArch: Fix and simplify fcsr initialization
 on execve)
To: Xi Ruoyao <xry111@xry111.site>
Cc: WANG Xuerui <kernel@xen0n.name>, Jiaxun Yang <jiaxun.yang@flygoat.com>, 
	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
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Tue, Jan 2, 2024 at 6:48=E2=80=AFPM Xi Ruoyao <xry111@xry111.site> wrote=
:
>
> 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.  I'm not sure how MIPS evades the is=
sue
> > > (or maybe it's just buggy too) but I'll investigate it later.
> >
> > Phew.  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.
> >
> > % cat measure.c
> > #include <fenv.h>
> > int main() { return fetestexcept(FE_INEXACT); }
> >
> > % echo $((1./3))
> > 0.33333333333333331
> >
> > % while ./a.out; do ; done
> > (stopped in seconds)
> >
> > 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.
> Maybe lose_fpu in SET_PERSONALITY2? But to me doing so will be really
> nasty.  Anyway I'll leave this for MIPS maintainers.
Disable preemption in SET_PERSONALITY2 and enable in START_THREAD?

Huacai

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