debian/patches/extra/0009-vga-make-display-updates-thread-safe.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Gerd Hoffmann <kraxel@redhat.com>
   3 Date: Fri, 21 Apr 2017 11:16:27 +0200
   4 Subject: [PATCH] vga: make display updates thread safe.
   5
   6 The vga code clears the dirty bits *after* reading the framebuffer
   7 memory.  So if the guest framebuffer updates hits the race window
   8 between vga reading the framebuffer and vga clearing the dirty bits
   9 vga will miss that update
  10
  11 Fix it by using the new memory_region_copy_and_clear_dirty()
  12 memory_region_copy_get_dirty() functions.  That way we clear the
  13 dirty bitmap before reading the framebuffer.  Any guest display
  14 updates happening in parallel will be properly tracked in the
  15 dirty bitmap then and the next display refresh will pick them up.
  16
  17 Problem triggers with mttcg only.  Before mttcg was merged tcg
  18 never ran in parallel to vga emulation.  Using kvm will hide the
  19 problem too, due to qemu operating on a userspace copy of the
  20 kernel's dirty bitmap.
  21
  22 Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
  23 Message-id: 20170421091632.30900-5-kraxel@redhat.com
  24 Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
  25 ---
  26  hw/display/vga.c | 36 +++++++++++++++++-------------------
  27  1 file changed, 17 insertions(+), 19 deletions(-)
  28
  29 diff --git a/hw/display/vga.c b/hw/display/vga.c
  30 index 3991b88aac..b2516c8d21 100644
  31 --- a/hw/display/vga.c
  32 +++ b/hw/display/vga.c
  33 @@ -1465,7 +1465,8 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
  34      DisplaySurface *surface = qemu_console_surface(s->con);
  35      int y1, y, update, linesize, y_start, double_scan, mask, depth;
  36      int width, height, shift_control, line_offset, bwidth, bits;
  37 -    ram_addr_t page0, page1, page_min, page_max;
  38 +    ram_addr_t page0, page1;
  39 +    DirtyBitmapSnapshot *snap = NULL;
  40      int disp_width, multi_scan, multi_run;
  41      uint8_t *d;
  42      uint32_t v, addr1, addr;
  43 @@ -1480,9 +1481,6 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
  44
  45      full_update |= update_basic_params(s);
  46
  47 -    if (!full_update)
  48 -        vga_sync_dirty_bitmap(s);
  49 -
  50      s->get_resolution(s, &width, &height);
  51      disp_width = width;
  52
  53 @@ -1625,11 +1623,17 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
  54      addr1 = (s->start_addr * 4);
  55      bwidth = (width * bits + 7) / 8;
  56      y_start = -1;
  57 -    page_min = -1;
  58 -    page_max = 0;
  59      d = surface_data(surface);
  60      linesize = surface_stride(surface);
  61      y1 = 0;
  62 +
  63 +    if (!full_update) {
  64 +        vga_sync_dirty_bitmap(s);
  65 +        snap = memory_region_snapshot_and_clear_dirty(&s->vram, addr1,
  66 +                                                      bwidth * height,
  67 +                                                      DIRTY_MEMORY_VGA);
  68 +    }
  69 +
  70      for(y = 0; y < height; y++) {
  71          addr = addr1;
  72          if (!(s->cr[VGA_CRTC_MODE] & 1)) {
  73 @@ -1644,17 +1648,17 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
  74          update = full_update;
  75          page0 = addr;
  76          page1 = addr + bwidth - 1;
  77 -        update |= memory_region_get_dirty(&s->vram, page0, page1 - page0,
  78 -                                          DIRTY_MEMORY_VGA);
  79 +        if (full_update) {
  80 +            update = 1;
  81 +        } else {
  82 +            update = memory_region_snapshot_get_dirty(&s->vram, snap,
  83 +                                                      page0, page1 - page0);
  84 +        }
  85          /* explicit invalidation for the hardware cursor (cirrus only) */
  86          update |= vga_scanline_invalidated(s, y);
  87          if (update) {
  88              if (y_start < 0)
  89                  y_start = y;
  90 -            if (page0 < page_min)
  91 -                page_min = page0;
  92 -            if (page1 > page_max)
  93 -                page_max = page1;
  94              if (!(is_buffer_shared(surface))) {
  95                  vga_draw_line(s, d, s->vram_ptr + addr, width);
  96                  if (s->cursor_draw_line)
  97 @@ -1687,13 +1691,7 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
  98          dpy_gfx_update(s->con, 0, y_start,
  99                         disp_width, y - y_start);
 100      }
 101 -    /* reset modified pages */
 102 -    if (page_max >= page_min) {
 103 -        memory_region_reset_dirty(&s->vram,
 104 -                                  page_min,
 105 -                                  page_max - page_min,
 106 -                                  DIRTY_MEMORY_VGA);
 107 -    }
 108 +    g_free(snap);
 109      memset(s->invalidated_y_table, 0, sizeof(s->invalidated_y_table));
 110  }
 111
 112 --
 113 2.11.0
 114