linux-kernel - Re: [PATCH V3] LoongArch: Provide kernel fpu functions

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Message-ID: <59f11842359f8b3330ea036ca0bf6d5776e4870a.camel@xry111.site>
Date:   Mon, 06 Mar 2023 21:00:33 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     Huacai Chen <chenhuacai@...nel.org>, maobibo <maobibo@...ngson.cn>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Arnd Bergmann <arnd@...db.de>, loongarch@...ts.linux.dev,
        linux-arch@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
        Guo Ren <guoren@...nel.org>, Xuerui Wang <kernel@...0n.name>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-kernel@...r.kernel.org, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH V3] LoongArch: Provide kernel fpu functions

On Mon, 2023-03-06 at 20:49 +0800, Huacai Chen wrote:
> > > +     if (!is_fpu_owner())
> > > +             enable_fpu();
> > > +     else
> > > +             _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...
-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University