[PATCH] fix screen corruption bug in vga_draw_graphic()

[Andreas Winkelbauer <andreas.winkelbauer@gmx.at>]

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hi,

the attached patch fixes the screen corruption issues which were 
reported by others, see:

http://article.gmane.org/gmane.comp.emulators.kvm.devel/13543
http://article.gmane.org/gmane.comp.emulators.kvm.devel/13409

The bug is kvm specific and can only be observed in graphics mode using 
relatively high resolutions (when one line uses more than one page of 
memory). As far as I've seen this bug is around since commit 
dd9591e0fea25a1414f4a6b2faa61ed733e0acc6 (5 nov 2006).

I've attached two versions of the patch. One just changes the relevant 
line and the other one also cleans up formatting (indention) of the kvm 
specific code.

cheers,
Andi

[-- Attachment #2: vga_draw_graphic.patch --]
[-- Type: text/x-patch, Size: 1489 bytes --]

--- kvm-61.orig/qemu/hw/vga.c	2008-02-19 15:58:28.000000000 +0100
+++ kvm-61/qemu/hw/vga.c	2008-02-22 20:46:14.000000000 +0100
@@ -1558,17 +1558,20 @@ static void vga_draw_graphic(VGAState *s
         update = full_update |
             cpu_physical_memory_get_dirty(page0, VGA_DIRTY_FLAG) |
             cpu_physical_memory_get_dirty(page1, VGA_DIRTY_FLAG);
-	if (kvm_enabled()) {
-		update |= bitmap_get_dirty(bitmap, (page0 - s->vram_offset) >> TARGET_PAGE_BITS);
-		update |= bitmap_get_dirty(bitmap, (page1 - s->vram_offset) >> TARGET_PAGE_BITS);
-	}
+        if (kvm_enabled()) {
+            update |= bitmap_get_dirty(bitmap,
+                (page0 - s->vram_offset) >> TARGET_PAGE_BITS);
+            update |= bitmap_get_dirty(bitmap,
+                (page1 - s->vram_offset) >> TARGET_PAGE_BITS);
+        }
 
         if ((page1 - page0) > TARGET_PAGE_SIZE) {
             /* if wide line, can use another page */
             update |= cpu_physical_memory_get_dirty(page0 + TARGET_PAGE_SIZE,
                                                     VGA_DIRTY_FLAG);
-	    if (kvm_enabled())
-		update |= bitmap_get_dirty(bitmap, (page0 - s->vram_offset) >> TARGET_PAGE_BITS);
+        if (kvm_enabled())
+            update |= bitmap_get_dirty(bitmap, (page0 + TARGET_PAGE_SIZE
+                - s->vram_offset) >> TARGET_PAGE_BITS);
         }
         /* explicit invalidation for the hardware cursor */
         update |= (s->invalidated_y_table[y >> 5] >> (y & 0x1f)) & 1;

[-- Attachment #3: vga_draw_graphic-no_formatting_changes.patch --]
[-- Type: text/x-patch, Size: 696 bytes --]

--- kvm-61.orig/qemu/hw/vga.c	2008-02-19 15:58:28.000000000 +0100
+++ kvm-61/qemu/hw/vga.c	2008-02-22 21:01:19.000000000 +0100
@@ -1568,7 +1568,7 @@ static void vga_draw_graphic(VGAState *s
             update |= cpu_physical_memory_get_dirty(page0 + TARGET_PAGE_SIZE,
                                                     VGA_DIRTY_FLAG);
 	    if (kvm_enabled())
-		update |= bitmap_get_dirty(bitmap, (page0 - s->vram_offset) >> TARGET_PAGE_BITS);
+		update |= bitmap_get_dirty(bitmap, (page0 + TARGET_PAGE_SIZE - s->vram_offset) >> TARGET_PAGE_BITS);
         }
         /* explicit invalidation for the hardware cursor */
         update |= (s->invalidated_y_table[y >> 5] >> (y & 0x1f)) & 1;

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