On Sun, 2021-10-24 at 21:25 -0400, Jason Andryuk wrote:
> commit fcacdfbef5a1 ("PCI/MSI: Provide a new set of mask and unmask
> functions") introduce functions pci_msi_update_mask() and
> pci_msix_write_vector_ctrl() that is missing checks for
> pci_msi_ignore_mask that exists in commit 446a98b19fd6 ("PCI/MSI: Use
> new mask/unmask functions").  The checks are in place at the high level
> __pci_msi_mask_desc()/__pci_msi_unmask_desc(), but some functions call
> directly to the helpers.
> 
> Push the pci_msi_ignore_mask check down to the functions that make
> the actual writes.  This keeps the logic local to the writes that need
> to be bypassed.
> 
> With Xen PV, the hypervisor is responsible for masking and unmasking the
> interrupts, which pci_msi_ignore_mask is used to indicate.

This isn't just for Xen PV; Xen HVM guests let Xen unmask the MSI for
them too.