linux-kernel - [PATCH AUTOSEL 4.19 095/172] vfio-pci: Mask cap zero

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Message-Id: <20200618012218.607130-95-sashal@kernel.org>
Date:   Wed, 17 Jun 2020 21:21:01 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Sasha Levin <sashal@...nel.org>, kvm@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 095/172] vfio-pci: Mask cap zero

From: Alex Williamson <alex.williamson@...hat.com>

[ Upstream commit bc138db1b96264b9c1779cf18d5a3b186aa90066 ]

The PCI Code and ID Assignment Specification changed capability ID 0
from reserved to a NULL capability in the v1.1 revision.  The NULL
capability is defined to include only the 16-bit capability header,
ie. only the ID and next pointer.  Unfortunately vfio-pci creates a
map of config space, where ID 0 is used to reserve the standard type
0 header.  Finding an actual capability with this ID therefore results
in a bogus range marked in that map and conflicts with subsequent
capabilities.  As this seems to be a dummy capability anyway and we
already support dropping capabilities, let's hide this one rather than
delving into the potentially subtle dependencies within our map.

Seen on an NVIDIA Tesla T4.

Reviewed-by: Cornelia Huck <cohuck@...hat.com>
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/vfio/pci/vfio_pci_config.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index c2d300bc37f6..36bc8f104e42 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -1464,7 +1464,12 @@ static int vfio_cap_init(struct vfio_pci_device *vdev)
 		if (ret)
 			return ret;

-		if (cap <= PCI_CAP_ID_MAX) {
+		/*
+		 * ID 0 is a NULL capability, conflicting with our fake
+		 * PCI_CAP_ID_BASIC.  As it has no content, consider it
+		 * hidden for now.
+		 */
+		if (cap && cap <= PCI_CAP_ID_MAX) {
 			len = pci_cap_length[cap];
 			if (len == 0xFF) { /* Variable length */
 				len = vfio_cap_len(vdev, cap, pos);
-- 
2.25.1