Re: [Qemu-devel] [PATCH 20/40] pci: use memory core for iommu support

[Peter Maydell]

On 11 May 2013 06:09, liu ping fan <address@hidden> wrote:
> On Wed, May 8, 2013 at 2:30 AM, Peter Maydell <address@hidden> wrote:
>> Also, technically speaking get_system_memory() is never the
>> right answer, though in practice it's good enough for our
>> purposes. (returning get_system_memory() would allow a bus
>> master DMA device to access back into the PCI bus by
>> DMAing to the address in system memory where the PCI host
>> controller is mapped, which I'm guessing is not possible
>> on real hardware.)
>>
> I think although it is rare case, but PCI device can fetch another's
> data on its pci-ram, expecially pci-spec does not forbid it.

Yes, certainly, but this happens because the other pci device
is present in the PCI address space, not because PCI device
A talks to the host controller's CPU-facing interface and
accesses PCI device B that way...

-- PMM