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From: Richard Henderson <richard.henderson@linaro.org>
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Date: Wed, 28 Mar 2018 10:26:30 +0800
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Subject: Re: [Qemu-devel] [PATCH v1 1/1] RISC-V: Workaround for critical
 mstatus.FS MTTCG bug
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To: Michael Clark <mjc@sifive.com>, =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <f4bug@amsat.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, Peter Maydell <peter.maydell@linaro.org>, Sagar Karandikar <sagark@eecs.berkeley.edu>, Bastian Koppelmann <kbastian@mail.uni-paderborn.de>, Palmer Dabbelt <palmer@sifive.com>, RISC-V Patches <patches@groups.riscv.org>

On 03/28/2018 08:15 AM, Michael Clark wrote:
> On looking at this again, I think we may need to remove
> the qemu_tcg_mttcg_enabled conditional and always return dirty if the state is
> initial or clean, but not off.

Yes.

> While testing on uniprocessor worked okay, it's likely because we were lucky
> and there was no task migration or multiple FPU tasks working.

Also yes.

>     > +        if (qemu_tcg_mttcg_enabled()) {
>     > +            /* FP is always dirty or off */
>     > +            if (mstatus & MSTATUS_FS) {
>     > +                mstatus |= MSTATUS_FS;
>     > +            }
>     > +        }

I've just posted an alternate patch set to track MSTATUS_FS more exactly, but
if that's thought to be too much this late in the cycle, then I'll sign off on
this patch without the mttcg test.


r~