linux-kernel - Re: [PATCH v2 1/5] nds32: nds32 FPU port

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Message-ID: <CAK8P3a1zQD7A40f6xfqW72e+ygDSKvYCJMb4=WjDRVo9au5syA@mail.gmail.com>
Date:   Fri, 12 Oct 2018 11:22:40 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Vincent Chen <vincentc@...estech.com>
Cc:     Vincent Chen <deanbo422@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greentime Hu <green.hu@...il.com>
Subject: Re: [PATCH v2 1/5] nds32: nds32 FPU port

On Fri, Oct 12, 2018 at 10:52 AM Vincent Chen <vincentc@...estech.com> wrote:
>
> On Thu, Oct 11, 2018 at 03:30:30PM +0800, Arnd Bergmann wrote:
> > On Thu, Oct 11, 2018 at 4:56 AM Vincent Chen <vincentc@...estech.com> wrote:

> > There was a long discussion on RISC-V about what happens when
> > FPU support is enabled or disabled, you may have seen that as well.
> >
> > Can you confirm that:
> >
> > a) A kernel with FPU support enabled running on a CPU without an FPU
> >     will behave the same as a kernel without FPU support, and in particular
> >     not crash while trying to access the FPU
> > b) A kernel with FPU support disabled running on a CPU with an FPU
> >     prevents user space from accessing the FPU, to avoid corrupting
> >     FPU registers during a task switch when a process accidentally contains
> >     FPU access
>
> In this patch user program will be terminated when accessing FPU register
> if the FPU support is disabled on kernel. Hence, condition b) is promised.
> Condition a) is unsupported in this patch. I will add this support in
> the next version patch.

Ok, sounds good, thanks

  Arnd