[kvmtool,v2] vfio: fix multi-MSI vector handling

Commit Message

Lorenzo Pieralisi April 24, 2020, 3:31 p.m. UTC

A PCI device with a MSI capability enabling Multiple MSI messages
(through the Multiple Message Enable field in the Message Control
register[6:4]) is expected to drive the Message Data lower bits (number
determined by the number of selected vectors) to generate the
corresponding MSI messages writes on the PCI bus.

Therefore, KVM expects the MSI data lower bits (a number of
bits that depend on bits [6:4] of the Message Control
register - which in turn control the number of vectors
allocated) to be set-up by kvmtool while programming the
MSI IRQ routing entries to make sure the MSI entries can
actually be demultiplexed by KVM and IRQ routes set-up
accordingly so that when an actual HW fires KVM can
route it to the correct entry in the interrupt controller
(and set-up a correct passthrough route for directly
injected interrupt).

Current kvmtool code does not set-up Message data entries
correctly for multi-MSI vectors - the data field is left
as programmed in the MSI capability by the guest for all
vector entries, triggering IRQs misrouting.

Fix it.

Signed-off-by: Lorenzo Pieralisi <[e-mail]>
Acked-by: Marc Zyngier <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: Julien Thierry <[e-mail]>
---
v1 -> v2:
	- Removed superfluous nr_vectors check
	- Added MarcZ ACK
	- Added comment

 vfio/pci.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Will Deacon April 24, 2020, 5:03 p.m. UTC | #1

On Fri, Apr 24, 2020 at 04:31:19PM +0100, Lorenzo Pieralisi wrote:
> A PCI device with a MSI capability enabling Multiple MSI messages
> (through the Multiple Message Enable field in the Message Control
> register[6:4]) is expected to drive the Message Data lower bits (number
> determined by the number of selected vectors) to generate the
> corresponding MSI messages writes on the PCI bus.
> 
> Therefore, KVM expects the MSI data lower bits (a number of
> bits that depend on bits [6:4] of the Message Control
> register - which in turn control the number of vectors
> allocated) to be set-up by kvmtool while programming the
> MSI IRQ routing entries to make sure the MSI entries can
> actually be demultiplexed by KVM and IRQ routes set-up
> accordingly so that when an actual HW fires KVM can
> route it to the correct entry in the interrupt controller
> (and set-up a correct passthrough route for directly
> injected interrupt).
> 
> Current kvmtool code does not set-up Message data entries
> correctly for multi-MSI vectors - the data field is left
> as programmed in the MSI capability by the guest for all
> vector entries, triggering IRQs misrouting.
> 
> Fix it.
> 
> Signed-off-by: Lorenzo Pieralisi <[e-mail]>
> Acked-by: Marc Zyngier <[e-mail]>
> Cc: Will Deacon <[e-mail]>
> Cc: Julien Thierry <[e-mail]>
> ---
> v1 -> v2:
> 	- Removed superfluous nr_vectors check
> 	- Added MarcZ ACK
> 	- Added comment

Thanks, pushed out now.

Will

Patch

diff --git a/vfio/pci.c b/vfio/pci.c
index 76e24c1..3c11b86 100644
--- a/vfio/pci.c
+++ b/vfio/pci.c
@@ -434,6 +434,14 @@  static void vfio_pci_msi_cap_write(struct kvm *kvm, struct vfio_device *vdev,
 
 	for (i = 0; i < nr_vectors; i++) {
 		entry = &pdev->msi.entries[i];
+
+		/*
+		 * Set the MSI data value as required by the PCI local
+		 * bus specifications, MSI capability, "Message Data".
+		 */
+		msg.data &= ~(nr_vectors - 1);
+		msg.data |= i;
+
 		entry->config.msg = msg;
 		vfio_pci_update_msi_entry(kvm, vdev, entry);
 	}