[vfio-users] PLX switch report a UR when EP tries to DMA to VM's memory

[Wuzongyong (Euler Dept)]

Hi,

I notice a problem with a PCIe endpoint, which is behind a PLX switch, assigned to a VM by VFIO.
The problem is switch report a UR error when the EP tries to DMA to a memory zone inside VM's address space.
Assume that the DMA destination address is between in the VM's ram address space, and unfortunately that
address value in host's point of view just hit the PLX switch  upstream port BAR0 memory-mapped IO range.
In a result, the DMA will failed because SW think this memory request is invalid if the destination address hit
its UP's bar.
Is this a hardware bug or qemu/seabios doesn't maintain a proper address space for VM?

Thanks,
Zongyong Wu

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