linux-kernel - [PATCH 10/19] iommu/vt-d: Don't copy translation tables if RTT bit needs to be changed

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Message-Id: <1434178047-17809-11-git-send-email-joro@8bytes.org>
Date:	Sat, 13 Jun 2015 08:47:18 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	iommu@...ts.linux-foundation.org
Cc:	David Woodhouse <dwmw2@...radead.org>, zhen-hual@...com,
	bhe@...hat.com, ddutile@...hat.com, alex.williamson@...hat.com,
	dyoung@...hat.com, linux-kernel@...r.kernel.org,
	jroedel@...tes.org, joro@...tes.org, Joerg Roedel <jroedel@...e.de>
Subject: [PATCH 10/19] iommu/vt-d: Don't copy translation tables if RTT bit needs to be changed

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

We can't change the RTT bit when translation is enabled, so
don't copy translation tables when we would change the bit
with our new root entry.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 drivers/iommu/intel-iommu.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 39bc3d6..e23d5b4 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -2914,10 +2914,20 @@ static int copy_translation_tables(struct intel_iommu *iommu)
 	unsigned long flags;
 	u64 rtaddr_reg;
 	int bus, ret;
-	bool ext;
+	bool new_ext, ext;
 
 	rtaddr_reg = dmar_readq(iommu->reg + DMAR_RTADDR_REG);
 	ext        = !!(rtaddr_reg & DMA_RTADDR_RTT);
+	new_ext    = !!ecap_ecs(iommu->ecap);
+
+	/*
+	 * The RTT bit can only be changed when translation is disabled,
+	 * but disabling translation means to open a window for data
+	 * corruption. So bail out and don't copy anything if we would
+	 * have to change the bit.
+	 */
+	if (new_ext != ext)
+		return -EINVAL;
 
 	old_rt_phys = rtaddr_reg & VTD_PAGE_MASK;
 	if (!old_rt_phys)
-- 
1.9.1

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