[PATCH v3 4/4] x86/msi: clear initial MSI-X state on boot

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

Some firmware/devices are found to not reset MSI-X properly, leaving
MASKALL set. Jason reports on his machine MASKALL persists through a
warm reboot, but is cleared on cold boot. Xen relies on initial state
being MASKALL clear. Especially, pci_reset_msix_state() assumes if
MASKALL is set, it was Xen setting it due to msix->host_maskall or
msix->guest_maskall. Clearing just MASKALL might be unsafe if ENABLE is
set, so clear them both.

Reported-by: Jason Andryuk <jandryuk@xxxxxxxxx>
Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
v3:
 - update comment
 - clear bits only when they were set
---
 xen/drivers/passthrough/msi.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/xen/drivers/passthrough/msi.c b/xen/drivers/passthrough/msi.c
index ce1a450f6f4a..c9f7eac29ebf 100644
--- a/xen/drivers/passthrough/msi.c
+++ b/xen/drivers/passthrough/msi.c
@@ -46,6 +46,23 @@ int pdev_msi_init(struct pci_dev *pdev)
         spin_lock_init(&msix->table_lock);
 
         ctrl = pci_conf_read16(pdev->sbdf, msix_control_reg(pos));
+
+        if ( ctrl & (PCI_MSIX_FLAGS_MASKALL|PCI_MSIX_FLAGS_ENABLE) )
+        {
+            /*
+             * pci_reset_msix_state() relies on MASKALL not being set
+             * initially, clear it (and ENABLE too - for safety), to meet that
+             * expectation.
+             */
+            printk(XENLOG_WARNING
+                   "%pp: unexpected initial MSI-X state (MASKALL=%d, 
ENABLE=%d), fixing\n",
+                   &pdev->sbdf,
+                   (ctrl & PCI_MSIX_FLAGS_MASKALL) ? 1 : 0,
+                   (ctrl & PCI_MSIX_FLAGS_ENABLE) ? 1 : 0);
+            ctrl &= ~(PCI_MSIX_FLAGS_ENABLE|PCI_MSIX_FLAGS_MASKALL);
+            pci_conf_write16(pdev->sbdf, msix_control_reg(pos), ctrl);
+        }
+
         msix->nr_entries = msix_table_size(ctrl);
 
         pdev->msix = msix;
-- 
git-series 0.9.1