RE: [RFC PATCH v3 3/5] PCI: Add host bridge attribute to indicate filtering of MSIs is supported

From: David Laight
Date: Fri Jan 15 2016 - 12:27:43 EST

From: Yongji Xie
> Sent: 15 January 2016 07:06
> MSI-X tables are not allowed to be mmapped in vfio-pci
> driver in case that user get to touch this directly.
> This will cause some performance issues when when PCI
> adapters have critical registers in the same page as
> the MSI-X table.
If the driver wants to generate an incorrect MSI-X interrupt
it can do so by requesting the device do a normal memory transfer
to the target address area that raises MSI-X interrupts.
So disabling writes to the MSI-X table (and pending bit array)
areas only raises the bar very slightly.
A device may also give the driver write access to the MSI-X
table through other addresses.

This seems to make disallowing the mapping of the MSI-X table
rather pointless.

I've also dumped out the MSI-X table (during development) to
check that the values are being written there correctly.