linux-kernel - [PATCH] vfio-pci: Mask cap zero

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Message-ID: <158836927527.9272.16785800801999547009.stgit@gimli.home>
Date:   Fri, 01 May 2020 15:41:24 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, cohuck@...hat.com
Subject: [PATCH] vfio-pci: Mask cap zero

There is no PCI spec defined capability with ID 0, therefore we don't
expect to find it in a capability chain and we use this index in an
internal array for tracking the sizes of various capabilities to handle
standard config space.  Therefore if a device does present us with a
capability ID 0, we mark our capability map with nonsense that can
trigger conflicts with other capabilities in the chain.  Ignore ID 0
when walking the capability chain, handling it as a hidden capability.

Seen on an NVIDIA Tesla T4.

Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
---
 drivers/vfio/pci/vfio_pci_config.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index 87d0cc8c86ad..5935a804cb88 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -1487,7 +1487,7 @@ static int vfio_cap_init(struct vfio_pci_device *vdev)
 		if (ret)
 			return ret;

-		if (cap <= PCI_CAP_ID_MAX) {
+		if (cap && cap <= PCI_CAP_ID_MAX) {
 			len = pci_cap_length[cap];
 			if (len == 0xFF) { /* Variable length */
 				len = vfio_cap_len(vdev, cap, pos);