linux-kernel - Re: arm64 syzbot instances

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Date:   Mon, 15 Mar 2021 11:01:45 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     John Garry <john.garry@...wei.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        syzkaller <syzkaller@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Maydell <peter.maydell@...aro.org>,
        Alex Bennée <alex.bennee@...aro.org>
Subject: Re: arm64 syzbot instances

On Mon, Mar 15, 2021 at 10:45 AM John Garry <john.garry@...wei.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?