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

[Li Qiang]

Peter Maydell <peter.maydell@linaro.org> 于2020年9月3日周四 下午6:53写道：
>
> 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

Here mean device A is an interrupt controller?
This is special case I think.

>   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

As the P2P is a normal behavior, we can't just prevent this.

Thanks,
Li Qiang
> can form loops. Self-DMA is just an easy way to find one
> category of these with the fuzzer.
>
> thanks
> -- PMM