[PATCH] drm/i915/opregion: rvda is relative from opregion base, not absolute

[Jani Nikula <jani.nikula@intel.com>]

We've supported the opregion RVDA/RVDS fields for VBT size >= 6 KB since
commit 04ebaadb9f2d ("drm/i915/opregion: handle VBT sizes bigger than 6
KB"). That's three years, almost to the date.

The implementation was based on spec only, in anticipation of systems
with big VBT. Now, the spec has been changed. The RVDA is supposed to be
relative from the beginning of opregion, not absolute address.

This is obviously a backward/forward incompatible change. I've been told
there are no systems out there using the field. Fingers crossed. This
will still be problematic for older kernels, and we can only try to
backport the fix.

Fixes: 04ebaadb9f2d ("drm/i915/opregion: handle VBT sizes bigger than 6 KB")
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
---
 drivers/gpu/drm/i915/intel_opregion.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_opregion.c b/drivers/gpu/drm/i915/intel_opregion.c
index b8f106d9ecf8..700fddaa8d9e 100644
--- a/drivers/gpu/drm/i915/intel_opregion.c
+++ b/drivers/gpu/drm/i915/intel_opregion.c
@@ -119,7 +119,7 @@ struct opregion_asle {
 	u64 fdss;
 	u32 fdsp;
 	u32 stat;
-	u64 rvda;	/* Physical address of raw vbt data */
+	u64 rvda;	/* Address of raw vbt data, relative from opregion */
 	u32 rvds;	/* Size of raw vbt data */
 	u8 rsvd[58];
 } __packed;
@@ -955,7 +955,13 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
 
 	if (opregion->header->opregion_ver >= 2 && opregion->asle &&
 	    opregion->asle->rvda && opregion->asle->rvds) {
-		opregion->rvda = memremap(opregion->asle->rvda,
+		/*
+		 * rvda is unsigned, relative from opregion base, and should
+		 * never point within opregion.
+		 */
+		WARN_ON(opregion->asle->rvda < OPREGION_SIZE);
+
+		opregion->rvda = memremap(asls + opregion->asle->rvda,
 					  opregion->asle->rvds,
 					  MEMREMAP_WB);
 		vbt = opregion->rvda;
@@ -967,6 +973,8 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
 			goto out;
 		} else {
 			DRM_DEBUG_KMS("Invalid VBT in ACPI OpRegion (RVDA)\n");
+			memunmap(opregion->rvda);
+			opregion->rvda = NULL;
 		}
 	}
 
-- 
2.11.0

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