linux-kernel - [PATCH 3.2 12/52] iommu/vt-d: Fix ATSR handling for Root-Complex integrated endpoints

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Message-ID: <lsq.1448404439.360295070@decadent.org.uk>
Date:	Tue, 24 Nov 2015 22:33:59 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"David Woodhouse" <David.Woodhouse@...el.com>
Subject: [PATCH 3.2 12/52] iommu/vt-d: Fix ATSR handling for Root-Complex
 integrated endpoints

3.2.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: David Woodhouse <David.Woodhouse@...el.com>

commit d14053b3c714178525f22660e6aaf41263d00056 upstream.

The VT-d specification says that "Software must enable ATS on endpoint
devices behind a Root Port only if the Root Port is reported as
supporting ATS transactions."

We walk up the tree to find a Root Port, but for integrated devices we
don't find one — we get to the host bridge. In that case we *should*
allow ATS. Currently we don't, which means that we are incorrectly
failing to use ATS for the integrated graphics. Fix that.

We should never break out of this loop "naturally" with bus==NULL,
since we'll always find bridge==NULL in that case (and now return 1).

So remove the check for (!bridge) after the loop, since it can never
happen. If it did, it would be worthy of a BUG_ON(!bridge). But since
it'll oops anyway in that case, that'll do just as well.

Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
[bwh: Backported to 3.2:
 - Adjust context
 - There's no (!bridge) check to remove]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -3572,10 +3572,15 @@ found:
 	for (bus = dev->bus; bus; bus = bus->parent) {
 		struct pci_dev *bridge = bus->self;
 
-		if (!bridge || !pci_is_pcie(bridge) ||
+		/* If it's an integrated device, allow ATS */
+		if (!bridge)
+			return 1;
+		/* Connected via non-PCIe: no ATS */
+		if (!pci_is_pcie(bridge) ||
 		    bridge->pcie_type == PCI_EXP_TYPE_PCI_BRIDGE)
 			return 0;
 
+		/* If we found the root port, look it up in the ATSR */
 		if (bridge->pcie_type == PCI_EXP_TYPE_ROOT_PORT) {
 			for (i = 0; i < atsru->devices_cnt; i++)
 				if (atsru->devices[i] == bridge)

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