[PATCH 4.9 18/43] PCI/MSI: Enforce MSI[X] entry updates to be visible

[Sasha Levin]

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit b9255a7cb51754e8d2645b65dd31805e282b4f3e upstream.

Nothing enforces the posted writes to be visible when the function
returns. Flush them even if the flush might be redundant when the entry is
masked already as the unmask will flush as well. This is either setup or a
rare affinity change event so the extra flush is not the end of the world.

While this is more a theoretical issue especially the logic in the X86
specific msi_set_affinity() function relies on the assumption that the
update has reached the hardware when the function returns.

Again, as this never has been enforced the Fixes tag refers to a commit in:
   git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git

Fixes: f036d4ea5fa7 ("[PATCH] ia32 Message Signalled Interrupt support")
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Marc Zyngier <maz@xxxxxxxxxx>
Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>
Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20210729222542.515188147@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/pci/msi.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
index 3be9c0ceb4e9..77810f424049 100644
--- a/drivers/pci/msi.c
+++ b/drivers/pci/msi.c
@@ -341,6 +341,9 @@ void __pci_write_msi_msg(struct msi_desc *entry, struct msi_msg *msg)
 
 		if (unmasked)
 			__pci_msix_desc_mask_irq(entry, 0);
+
+		/* Ensure that the writes are visible in the device */
+		readl(base + PCI_MSIX_ENTRY_DATA);
 	} else {
 		int pos = dev->msi_cap;
 		u16 msgctl;
@@ -361,6 +364,8 @@ void __pci_write_msi_msg(struct msi_desc *entry, struct msi_msg *msg)
 			pci_write_config_word(dev, pos + PCI_MSI_DATA_32,
 					      msg->data);
 		}
+		/* Ensure that the writes are visible in the device */
+		pci_read_config_word(dev, pos + PCI_MSI_FLAGS, &msgctl);
 	}
 	entry->msg = *msg;
 }
-- 
2.30.2