diff --git a/ChangeLog b/ChangeLog
index 1d2a0fa8a..2d0473920 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2006-04-25  Eric Anholt  <anholt@FreeBSD.org>
+
+	* exa/exa_migration.c: (exaAssertNotDirty), (exaDoMigration):
+	* exa/exa_priv.h:
+	* hw/kdrive/ephyr/ephyr_draw.c: (exaDDXDriverInit):
+	Add an option to verify at the point of migration that pixmaps which
+	aren't marked dirty are in fact not dirty.  This will hopefully help
+	catch issues like the previous commit.  Leave it on in fakexa.
+
 2006-04-25  Eric Anholt  <anholt@FreeBSD.org>
 
 	* exa/exa_accel.c: (exaPutImage):
diff --git a/exa/exa_migration.c b/exa/exa_migration.c
index ef7cfd86e..8077f6802 100644
--- a/exa/exa_migration.c
+++ b/exa/exa_migration.c
@@ -406,6 +406,36 @@ exaMigrateTowardSys (PixmapPtr pPixmap)
 	exaMoveOutPixmap (pPixmap);
 }
 
+/**
+ * If the pixmap has both a framebuffer and system memory copy, this function
+ * asserts that both of them are the same.
+ */
+static void
+exaAssertNotDirty (PixmapPtr pPixmap)
+{
+    ExaPixmapPriv (pPixmap);
+    CARD8 *dst, *src;
+    int dst_pitch, src_pitch, data_row_bytes, y;
+
+    if (pExaPixmap == NULL || pExaPixmap->fb_ptr == NULL)
+	return;
+
+    dst = pExaPixmap->sys_ptr;
+    dst_pitch = pExaPixmap->sys_pitch;
+    src = pExaPixmap->fb_ptr;
+    src_pitch = pExaPixmap->fb_pitch;
+    data_row_bytes = pPixmap->drawable.width *
+		     pPixmap->drawable.bitsPerPixel / 8;
+
+    exaPrepareAccess(&pPixmap->drawable, EXA_PREPARE_SRC);
+    for (y = 0; y < pPixmap->drawable.height; y++) {
+	if (memcmp(dst, src, data_row_bytes) != 0) {
+	     abort();
+	}
+    }
+    exaFinishAccess(&pPixmap->drawable, EXA_PREPARE_SRC);
+}
+
 /**
  * Performs migration of the pixmaps according to the operation information
  * provided in pixmaps and can_accel and the migration scheme chosen in the
@@ -418,6 +448,19 @@ exaDoMigration (ExaMigrationPtr pixmaps, int npixmaps, Bool can_accel)
     ExaScreenPriv(pScreen);
     int i, j;
 
+    /* If this debugging flag is set, check each pixmap for whether it is marked
+     * as clean, and if so, actually check if that's the case.  This should help
+     * catch issues with failing to mark a drawable as dirty.  While it will
+     * catch them late (after the operation happened), it at least explains what
+     * went wrong, and instrumenting the code to find what operation happened
+     * to the pixmap last shouldn't be hard.
+     */
+    if (pExaScr->checkDirtyCorrectness) {
+	for (i = 0; i < npixmaps; i++) {
+	    if (!exaPixmapIsDirty (pixmaps[i].pPix))
+		exaAssertNotDirty (pixmaps[i].pPix);
+	}
+    }
     /* If anything is pinned in system memory, we won't be able to
      * accelerate.
      */
diff --git a/exa/exa_priv.h b/exa/exa_priv.h
index 89f8b0c9d..42c2f2d26 100644
--- a/exa/exa_priv.h
+++ b/exa/exa_priv.h
@@ -108,6 +108,7 @@ typedef struct {
     Bool			 swappedOut;
     enum ExaMigrationHeuristic	 migration;
     Bool			 hideOffscreenPixmapData;
+    Bool			 checkDirtyCorrectness;
 } ExaScreenPrivRec, *ExaScreenPrivPtr;
 
 /*
diff --git a/hw/kdrive/ephyr/ephyr_draw.c b/hw/kdrive/ephyr/ephyr_draw.c
index 0d095352f..0c1a5d0d3 100644
--- a/hw/kdrive/ephyr/ephyr_draw.c
+++ b/hw/kdrive/ephyr/ephyr_draw.c
@@ -515,4 +515,5 @@ exaDDXDriverInit(ScreenPtr pScreen)
 
     pExaScr->migration = ExaMigrationSmart;
     pExaScr->hideOffscreenPixmapData = TRUE;
+    pExaScr->checkDirtyCorrectness = TRUE;
 }