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In-Reply-To: <48347b4d-9194-16f2-95a0-c3eb55ca9a80@huawei.com>
From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Mon, 15 Mar 2021 11:01:45 +0100
Message-ID: <CACT4Y+a58QHkas=5t51Aou9GDHDtjyiGwtruUZgbe-iVmTp0Mw@mail.gmail.com>
Subject: Re: arm64 syzbot instances
To:     John Garry <john.garry@huawei.com>
Cc:     Arnd Bergmann <arnd@arndb.de>, Mark Rutland <mark.rutland@arm.com>,
        Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        syzkaller <syzkaller@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Maydell <peter.maydell@linaro.org>,
        =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>
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On Mon, Mar 15, 2021 at 10:45 AM John Garry <john.garry@huawei.com> wrote:
> >> It does not happen too often on syzbot so far, so let's try to do the
> >> right thing first.
> >> I've filed: https://bugs.launchpad.net/qemu/+bug/1918917
> >> with a link to this thread. To be fair, I don't fully understand what
> >> I am talking about, I hope I proxied your description properly.
> >
> > Thanks, looks good. I provided a little more detail in a comment there.
> >
> >          Arnd
> > .
> >
>
>  From looking at the bug report, my impression is that this is a qemu
> issue, as the logical IO space is mapped to the PCI host bridge IO
> space, and qemu does not handle accesses to that CPU addressable region
> at all. As Arnd said.
>
> However, we really should not be accessing logical IO ports 0 or 0x2f8
> at all via ttyS3 if not enumerated from PCI device at that logical IO
> port. That is what I think anyway, as who knows what device - if any -
> really exists at that location. That is why I had this patch to just
> stop accesses to legacy IO port regions on arm64:
>
> https://lore.kernel.org/lkml/1610729929-188490-2-git-send-email-john.garry@huawei.com/

Hi John,

Thanks for the info.

The patch is from January, but it's not merged yet, right?
It will fix the crash we see, right?