[PATCH v21 4/4] PCI/MSI: Enable memory decoding before restoring MSI-X messages

[Farhan Ali <alifm@linux.ibm.com>]

The current MSI-X restoration path assumes the Command register Memory bit
is enabled when writing MSI-X messages. But it's possible the last saved
and restored state of a device may not have the Memory bit enabled, even if
a device driver later enables Memory bit and MSI-X. Attempting to access
Memory space without Memory bit enabled can lead to Unsupported Request
(UR) from the device. Fix this by enabling Memory bit and restore it
afterwards.

Fixes: 41017f0cac92 ("[PATCH] PCI: MSI(X) save/restore for suspend/resume")
Cc: stable@vger.kernel.org
Reviewed-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
---
 drivers/pci/msi/msi.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/pci/msi/msi.c b/drivers/pci/msi/msi.c
index 209373c92e9e..79c7e84d314b 100644
--- a/drivers/pci/msi/msi.c
+++ b/drivers/pci/msi/msi.c
@@ -870,6 +870,7 @@ void __pci_restore_msix_state(struct pci_dev *dev)
 {
 	struct msi_desc *entry;
 	bool write_msg;
+	u16 cmd;
 
 	if (!dev->msix_enabled)
 		return;
@@ -879,6 +880,14 @@ void __pci_restore_msix_state(struct pci_dev *dev)
 	pci_msix_clear_and_set_ctrl(dev, 0,
 				PCI_MSIX_FLAGS_ENABLE | PCI_MSIX_FLAGS_MASKALL);
 
+	/*
+	 * The restored device state may not have Memory decoding enabled
+	 * in the Command register. Since the MSI-X was enabled for the
+	 * device, enable Memory decoding before restoring MSI-X.
+	 */
+	pci_read_config_word(dev, PCI_COMMAND, &cmd);
+	pci_write_config_word(dev, PCI_COMMAND, cmd | PCI_COMMAND_MEMORY);
+
 	write_msg = arch_restore_msi_irqs(dev);
 
 	scoped_guard (msi_descs_lock, &dev->dev) {
@@ -889,6 +898,7 @@ void __pci_restore_msix_state(struct pci_dev *dev)
 		}
 	}
 
+	pci_write_config_word(dev, PCI_COMMAND, cmd);
 	pci_msix_clear_and_set_ctrl(dev, PCI_MSIX_FLAGS_MASKALL, 0);
 }
 
-- 
2.43.0