linux-kernel - [PATCH] iommu/intel: GAW only gets smaller by adding devices

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Message-ID: <20140529202304.10925.20871.stgit@bling.home>
Date:	Thu, 29 May 2014 14:23:17 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	iommu@...ts.linux-foundation.org
Cc:	David Woodhouse <dwmw2@...radead.org>,
	linux-kernel@...r.kernel.org, mspeder@...rs.sourceforge.net
Subject: [PATCH] iommu/intel: GAW only gets smaller by adding devices

As analyzed in https://bugzilla.kernel.org/show_bug.cgi?id=76331
we can have multiple DRHDs in a system and each may support different
guest address widths.  We can add a device behind a less capable DRHD
to a domain so long as the lesser DRHD can map the existing domain
page table.  We should never increase the address width as a result
of adding a device to the domain.  The current code simply updates
the width to the last added device.  Change to keep it at the
minumum DRHD width.

Reported-by: mspeder@...rs.sourceforge.net
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
Cc: David Woodhouse <dwmw2@...radead.org>
---
 drivers/iommu/intel-iommu.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index e68f44b..cd41d8d 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -4276,7 +4276,7 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
 		       __func__, addr_width, dmar_domain->max_addr);
 		return -EFAULT;
 	}
-	dmar_domain->gaw = addr_width;
+	dmar_domain->gaw = min(addr_width, dmar_domain->gaw);
 
 	/*
 	 * Knock out extra levels of page tables if necessary

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