[PATCH] vfio-pci: Fix MSI IRQ forwarding for without per-vector masking

[Leo Yan <leo.yan@linaro.org>]

If MSI doesn't support per-vector masking capability and
PCI_MSI_FLAGS_MASKBIT isn't set in message control field, the function
vfio_pci_msi_vector_write() will directly bail out for this case and
every vector's 'virt_state' keeps setting bit VFIO_PCI_MSI_STATE_MASKED.

This results in the state maintained in 'virt_state' cannot really
reflect the MSI hardware state; finally it will mislead the function
vfio_pci_update_msi_entry() to skip IRQ forwarding with below flow:

vfio_pci_update_msi_entry() {

  [...]

  if (msi_is_masked(entry->virt_state) == msi_is_masked(entry->phys_state))
      return 0;  ==> skip IRQ forwarding

  [...]
}

To fix this issue, when detect PCI_MSI_FLAGS_MASKBIT is not set in the
message control field, this patch simply clears bit
VFIO_PCI_MSI_STATE_MASKED for all vectors 'virt_state'; at the end
vfio_pci_update_msi_entry() can forward MSI IRQ successfully.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 vfio/pci.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/vfio/pci.c b/vfio/pci.c
index ba971eb..4fd24ac 100644
--- a/vfio/pci.c
+++ b/vfio/pci.c
@@ -363,8 +363,18 @@ static int vfio_pci_msi_vector_write(struct kvm *kvm, struct vfio_device *vdev,
 	struct vfio_pci_device *pdev = &vdev->pci;
 	struct msi_cap_64 *msi_cap_64 = PCI_CAP(&pdev->hdr, pdev->msi.pos);
 
-	if (!(msi_cap_64->ctrl & PCI_MSI_FLAGS_MASKBIT))
+	if (!(msi_cap_64->ctrl & PCI_MSI_FLAGS_MASKBIT)) {
+		/*
+		 * If MSI doesn't support per-vector masking capability,
+		 * simply unmask for all vectors.
+		 */
+		for (i = 0; i < pdev->msi.nr_entries; i++) {
+			entry = &pdev->msi.entries[i];
+			msi_set_masked(entry->virt_state, false);
+		}
+
 		return 0;
+	}
 
 	if (msi_cap_64->ctrl & PCI_MSI_FLAGS_64BIT)
 		mask_pos = PCI_MSI_MASK_64;
-- 
2.19.1