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From:   Anup Patel <anup@brainfault.org>
Date:   Fri, 4 Sep 2020 19:26:41 +0530
Message-ID: <CAAhSdy2N8L015z0-RirjXLjdzt+OrCtzzKzivsMeQXoH9Nc8Cw@mail.gmail.com>
Subject: Re: [GIT PULL] RISC-V Fixes for 5.9-rc2
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Qiu Wenbo <qiuwenbo@kylinos.com.cn>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Sep 4, 2020 at 6:30 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Fri, Sep 04, 2020 at 08:58:25PM +0800, Qiu Wenbo wrote:
> > I can confirm this patch also breaks K210 support. It seems that
> > csr_read(CSR_TIME) will trigger an illegal instruction exception on K210.
>
> CSR_TIME is trapped by just about every implementation I know (which is
> explicitly allowed by the spec).  That is why we should never use it
> from common M-mode code.

Finally, I was able to replicate this issue by manually hacking QEMU to
not emulatie TIME CSR for virt machine.

It seems this issue is only seen on older QEMU and Kendrtye K210.

I am working on a fix for this issue.

Thanks for reporting.

Regards,
Anup