On Mon, Mar 15, 2021 at 11:31 AM John Garry <john.ga...@huawei.com> wrote: > > On 15/03/2021 10:01, Dmitry Vyukov wrote: > > On Mon, Mar 15, 2021 at 10:45 AM John Garry<john.ga...@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.ga...@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? > > . > > It's not merged, and it probably would solve this issue. But following > discussion with Arnd when it was originally posted, I still need to do > some analysis whether it is the proper thing to do.
OK, I will tell syzbot about the fixing patch. > However, as mentioned, the fundamental issue looks like qemu IO port > access, so it would be good to check that first. I've filed https://bugs.launchpad.net/qemu/+bug/1918917 for qemu. > On a related topic, I will cc colleague Jiahui Cen, who I think was > doing some work arm on qemu support in a related area, so may share some > experience here. > > Jiahui Cen did have a patch to fix logical PIO code from this work [0], > which is not merged, but I don't think would help here. I will cc you on it. > > Thanks, > John > > [0] > https://lore.kernel.org/lkml/006ad6ce-d6b2-59cb-8209-aca3f6e53...@huawei.com/