Re: [RFC 0/3] try to solve the DMA to MMIO issue

[Peter Maydell]

On Thu, 3 Sep 2020 at 04:55, Jason Wang <jasowang@redhat.com> wrote:
> I think we still need to seek a way to address this issue completely.
>
> How about adding a flag in MemoryRegionOps and detect the reentrancy
> through that flag?

This won't catch everything. Consider this situation:
  Device A makes DMA access to device B
  Device B's write-handling causes it to raise an
   outbound qemu_irq signal
  The qemu_irq signal is connected to device A
  Now we have reentered into device A's code

That is to say, the problem is general to "device A does
something that affects device B" links of all kinds, which
can form loops. Self-DMA is just an easy way to find one
category of these with the fuzzer.

thanks
-- PMM