vpci/msix: handle accesses adjacent to the MSI-X table

vpci/msix: handle accesses adjacent to the MSI-X table

The handling of the MSI-X table accesses by Xen requires that any
pages part of the MSI-X related tables are not mapped into the domain
physmap.  As a result, any device registers in the same pages as the
start or the end of the MSIX or PBA tables is not currently
accessible, as the accesses are just dropped.

Note the spec forbids such placing of registers, as the MSIX and PBA
tables must be 4K isolated from any other registers:

"If a Base Address register that maps address space for the MSI-X
Table or MSI-X PBA also maps other usable address space that is not
associated with MSI-X structures, locations (e.g., for CSRs) used in
the other address space must not share any naturally aligned 4-KB
address range with one where either MSI-X structure resides."

Yet the 'Intel Wi-Fi 6 AX201' device on one of my boxes has registers
in the same page as the MSIX tables, and thus won't work on a PVH dom0
without this fix.

In order to cope with the behavior passthrough any accesses that fall
on the same page as the MSIX tables (but don't fall in between) to the
underlying hardware.  Such forwarding also takes care of the PBA
accesses, so it allows to remove the code doing this handling in
msix_{read,write}.  Note that as a result accesses to the PBA array
are no longer limited to 4 and 8 byte sizes, there's no access size
restriction for PBA accesses documented in the specification.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
vpci/msix: restore PBA access length and alignment restrictions

Accesses to the PBA array have the same length and alignment
limitations as accesses to the MSI-X table:

"For all accesses to MSI-X Table and MSI-X PBA fields, software must
use aligned full DWORD or aligned full QWORD transactions; otherwise,
the result is undefined."

Introduce such length and alignment checks into the handling of PBA
accesses for vPCI.  This was a mistake of mine for not reading the
specification correctly.

Note that accesses must now be aligned, and hence there's no longer a
need to check that the end of the access falls into the PBA region as
both the access and the region addresses must be aligned.

Fixes: b177892d2d ('vpci/msix: handle accesses adjacent to the MSI-X table')
Reported-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: b177892d2d0e8a31122c218989f43130aeba5282
master date: 2023-03-28 14:20:35 +0200
master commit: 7a502b4fbc339e9d3d3d45fb37f09da06bc3081c
master date: 2023-03-29 14:56:33 +0200