Message-ID: <59f11842359f8b3330ea036ca0bf6d5776e4870a.camel@xry111.site>
Subject: Re: [PATCH V3] LoongArch: Provide kernel fpu functions
From:   Xi Ruoyao <xry111@xry111.site>
To:     Huacai Chen <chenhuacai@kernel.org>, maobibo <maobibo@loongson.cn>
Cc:     Huacai Chen <chenhuacai@loongson.cn>,
        Arnd Bergmann <arnd@arndb.de>, loongarch@lists.linux.dev,
        linux-arch@vger.kernel.org, Xuefeng Li <lixuefeng@loongson.cn>,
        Guo Ren <guoren@kernel.org>, Xuerui Wang <kernel@xen0n.name>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        linux-kernel@vger.kernel.org, loongson-kernel@lists.loongnix.cn
Date:   Mon, 06 Mar 2023 21:00:33 +0800
In-Reply-To: <CAAhV-H6_-iVAK6-MmfJq12JBzD6nyYNOiObEbzu8yzew3raAvg@mail.gmail.com>
References: <20230306095934.609589-1-chenhuacai@loongson.cn>
         <029a5993-b993-ab73-0a14-0df9b0ddf3da@loongson.cn>
         <CAAhV-H6_-iVAK6-MmfJq12JBzD6nyYNOiObEbzu8yzew3raAvg@mail.gmail.com>
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On Mon, 2023-03-06 at 20:49 +0800, Huacai Chen wrote:
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 if (!is_fpu_owner())
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 enable_fpu();
> > > +=C2=A0=C2=A0=C2=A0=C2=A0 else
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 _save_fp(&current->thread.fpu);
> > Do we need initialize fcsr rather than using random fcsr value
> > of other processes? There may be fpu exception enabled by
> > other tasks.
> Emm, I think initialize fcsr to 0 is better here.

I guess it's necessary: if we use a "dirty" FSCR0 with some exceptions
enabled (esp. inaccurate exception which is expected as disabled by most
developers), we may end up oops with a kernel FPE...
--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University