MSI-X: avoid array overrun upon MSI-X table writes

MSI-X: avoid array overrun upon MSI-X table writes

pt_msix_init() allocates msix->msix_entry[] to just cover
msix->total_entries entries. While pci_msix_readl() resorts to reading
physical memory for out of bounds reads, pci_msix_writel() so far
simply accessed/corrupted unrelated memory.

pt_iomem_map()'s call to cpu_register_physical_memory() registers a
page granular region, which is necessary as the Pending Bit Array may
share space with the MSI-X table (but nothing else is allowed to). This
also explains why pci_msix_readl() actually honors out of bounds reads,
but pci_msi_writel() doesn't need to.

This is XSA-164.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
(cherry picked from commit 569eac99e8ddccd15fe78e8a3af5622afe780e3b)