On Fri, Mar 12, 2021 at 9:46 AM Dmitry Vyukov <dvyu...@google.com> wrote: > On Fri, Mar 12, 2021 at 9:40 AM Arnd Bergmann <a...@arndb.de> wrote: > > On Thu, Mar 11, 2021 at 6:57 PM Dmitry Vyukov <dvyu...@google.com> wrote: > > a) accessing a legacy ISA/LPC port should not result in an oops, > > but should instead return values with all bits set. There could > > be a ratelimited console warning about broken drivers, but we > > can't assume that all drivers work correctly, as some ancient > > PC style drivers still rely on this. > > John Garry has recently worked on a related bugfix, so maybe > > either this is the same bug he encountered (and hasn't merged > > yet), or if his fix got merged there is still a remaining problem.
> > b) It should not be possible to open /dev/ttyS3 if the device is > > not initialized. What is the output of 'cat /proc/tty/driver/serial' > > on this machine? Do you see any messages from the serial > > driver in the boot log? > > Unfortunately there are so many different ways to probe devices > > in the 8250 driver that I don't know where this comes from. > > Your config file has > > CONFIG_SERIAL_8250_PNP=y > > CONFIG_SERIAL_8250_NR_UARTS=32 > > CONFIG_SERIAL_8250_RUNTIME_UARTS=4 > > CONFIG_SERIAL_8250_EXTENDED=y > > I guess it's probably the preconfigured uarts that somehow > > become probed without initialization, but it could also be > > an explicit device incorrectly described by qemu. > > > Here is fool boot log, /proc/tty/driver/serial and the crash: > https://gist.githubusercontent.com/dvyukov/084890d9b4aa7cd54f468e652a9b5881/raw/54c12248ff6a4885ba6c530d56b3adad59bc6187/gistfile1.txt Ok, so there are four 8250 ports, and none of them are initialized, while the console is on /dev/ttyAMA0 using a different driver. I'm fairly sure this is a bug in the kernel then, not in qemu. I also see that the PCI I/O space gets mapped to a physical address: [ 3.974309][ T1] pci-host-generic 4010000000.pcie: IO 0x003eff0000..0x003effffff -> 0x0000000000 So it's probably qemu that triggers the 'synchronous external abort' when accessing the PCI I/O space, which in turn hints towards a bug in qemu. Presumably it only returns data from I/O ports that are actually mapped to a device when real hardware is supposed to return 0xffffffff when reading from unused I/O ports. This would be separate from the work that John did, which only fixed the kernel for accessing I/O port ranges that do not have a corresponding MMU mapping to hardware ports. Arnd
