[PATCH 15/21] drm/i915: fix memory corruption with GM965 and >4GB RAM

[Jan Niehusmann]

commit 6927faf30920b8c03dfa007e732642a1f1f20089 upstream.

On a Thinkpad x61s, I noticed some memory corruption when
plugging/unplugging the external VGA connection. The symptoms are that
4 bytes at the beginning of a page get overwritten by zeroes.
The address of the corruption varies when rebooting the machine, but
stays constant while it's running (so it's possible to repeatedly write
some data and then corrupt it again by plugging the cable).

Further investigation revealed that the corrupted address is
(dev_priv->status_page_dmah->busaddr & 0xffffffff), ie. the beginning of
the hardware status page of the i965 graphics card, cut to 32 bits.

So it seems that for some memory access, the hardware uses only 32 bit
addressing. If the hardware status page is located >4GB, this
corrupts unrelated memory.

Signed-off-by: Jan Niehusmann <jan@xxxxxxxxxx>
Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
[bwh: Backport to 2.6.33]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/i915_dma.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index c93c98a..be27acc 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1411,6 +1411,17 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 	if (IS_GEN2(dev))
 		pci_set_consistent_dma_mask(dev->pdev, DMA_BIT_MASK(30));

+	/* 965GM sometimes incorrectly writes to hardware status page (HWS)
+	 * using 32bit addressing, overwriting memory if HWS is located
+	 * above 4GB.
+	 *
+	 * The documentation also mentions an issue with undefined
+	 * behaviour if any general state is accessed within a page above 4GB,
+	 * which also needs to be handled carefully.
+	 */
+	if (IS_I965G(dev) && !IS_G4X(dev) && !IS_IRONLAKE(dev))
+		pci_set_consistent_dma_mask(dev->pdev, DMA_BIT_MASK(32));
+
 	dev_priv->regs = ioremap(base, size);
 	if (!dev_priv->regs) {
 		DRM_ERROR("failed to map registers\n");
--
1.7.0.4

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