[PATCH] fix screen corruption bug in vga_draw_graphic()

[PATCH] fix screen corruption bug in vga_draw_graphic()

[Andreas Winkelbauer]

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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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Re: [PATCH] fix screen corruption bug in vga_draw_graphic()

[Avi Kivity]

Andreas Winkelbauer wrote:
> 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.

Applied the no-formatting version, thanks.  Please sign off on patches 
next time.

The way to apply formatting changes while fixing something is with a 
separate patch that does nothing but fix the formatting, either on top 
of the fix, or to be applied before the fix.  This way the fixing patch 
is kept small and easily understandable.


-- 
error compiling committee.c: too many arguments to function


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Re: [PATCH] fix screen corruption bug in vga_draw_graphic()

[Arne Brutschy]

Hey,

this patch works like a charm! No pointer trails, no bars through
dialogs... Perfect quality. Thanks alot Andreas!

Arne

On Fr, 2008-02-22 at 21:36 +0100, Andreas Winkelbauer wrote:
> 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


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