Re: arm64 syzbot instances

From: Peter Maydell
Date: Sat Mar 20 2021 - 16:44:27 EST

On Fri, 12 Mar 2021 at 09:16, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> 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.

Do you have a reference to the bit of the PCI spec that mandates
this -1/discard behaviour for attempted access to places where
there isn't actually a PCI device mapped ? The spec is pretty
long and hard to read...

(Knowing to what extent this behaviour is mandatory for all
PCI systems/host controllers vs just "it would be nice if the
gpex host controller worked this way" would help in figuring
out where in QEMU to change.)

-- PMM