linux-kernel - [PATCH] PCI: Don't use SR-IOV lock for ATS

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Date:	Thu, 18 Jun 2015 10:50:20 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Gregor Dick <gdick@...arflare.com>, linux-pci@...r.kernel.org,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Joerg Roedel <jroedel@...e.de>, stable@...nel.org
Subject: [PATCH] PCI: Don't use SR-IOV lock for ATS

From: Joerg Roedel <jroedel@...e.de>

The use of the SR-IOV lock for ATS causes a dead-lock in the
AMD-IOMMU driver when virtual functions are added that have
an ATS capability.

The problem is that the VFs will be added to the bus with
the SR-IOV lock held. While added to the bus the
device-notifiers will run and invoke AMD IOMMU code, which
itself will assign the device to a domain try to enable ATS.
When it calls pci_enable_ats() this will dead-lock.

Fix this by introducing a global ats_lock. ATS enablement
and disablement isn't in any fast-path, so a global lock
shouldn't hurt here.

Cc: stable@...nel.org
Reported-by: Gregor Dick <gdick@...arflare.com>
Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 drivers/pci/ats.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index a8099d4..f0c3c6f 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -17,6 +17,8 @@
 
 #include "pci.h"
 
+static DEFINE_MUTEX(ats_lock);
+
 static int ats_alloc_one(struct pci_dev *dev, int ps)
 {
 	int pos;
@@ -67,7 +69,7 @@ int pci_enable_ats(struct pci_dev *dev, int ps)
 	if (dev->is_physfn || dev->is_virtfn) {
 		struct pci_dev *pdev = dev->is_physfn ? dev : dev->physfn;
 
-		mutex_lock(&pdev->sriov->lock);
+		mutex_lock(&ats_lock);
 		if (pdev->ats)
 			rc = pdev->ats->stu == ps ? 0 : -EINVAL;
 		else
@@ -75,7 +77,7 @@ int pci_enable_ats(struct pci_dev *dev, int ps)
 
 		if (!rc)
 			pdev->ats->ref_cnt++;
-		mutex_unlock(&pdev->sriov->lock);
+		mutex_unlock(&ats_lock);
 		if (rc)
 			return rc;
 	}
@@ -116,11 +118,11 @@ void pci_disable_ats(struct pci_dev *dev)
 	if (dev->is_physfn || dev->is_virtfn) {
 		struct pci_dev *pdev = dev->is_physfn ? dev : dev->physfn;
 
-		mutex_lock(&pdev->sriov->lock);
+		mutex_lock(&ats_lock);
 		pdev->ats->ref_cnt--;
 		if (!pdev->ats->ref_cnt)
 			ats_free_one(pdev);
-		mutex_unlock(&pdev->sriov->lock);
+		mutex_unlock(&ats_lock);
 	}
 
 	if (!dev->is_physfn)
-- 
1.9.1

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