Another patch that seems to work tries to remember the old surface:

diff --git a/hw/display/vga.c b/hw/display/vga.c
index ed476e4e80..1aae6a6d3b 100644
--- a/hw/display/vga.c
+++ b/hw/display/vga.c
@@ -1554,7 +1554,8 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
         height != s->last_height ||
         s->last_depth != depth ||
         s->last_byteswap != byteswap ||
-        share_surface != is_buffer_shared(surface)) {
+        share_surface != is_buffer_shared(surface) ||
+        s->last_surface != surface) {
         /* display parameters changed -> need new display surface */
         s->last_scr_width = disp_width;
         s->last_scr_height = height;
@@ -1563,8 +1564,10 @@ static void vga_draw_graphic(VGACommonState *s, int full_update)
         s->last_line_offset = s->line_offset;
         s->last_depth = depth;
         s->last_byteswap = byteswap;
+        s->last_surface = surface;
         full_update = 1;
     }
+    fprintf(stderr, "%p vs %p   share_surface: %d   surface: %p\n", surface_data(surface), s->vram_ptr + (s->start_addr * 4), share_surface, surface);
     if (surface_data(surface) != s->vram_ptr + (s->start_addr * 4)
         && is_buffer_shared(surface)) {
         /* base address changed (page flip) -> shared display surfaces
diff --git a/hw/display/vga_int.h b/hw/display/vga_int.h
index f8fcf62a56..91afc52b0e 100644
--- a/hw/display/vga_int.h
+++ b/hw/display/vga_int.h
@@ -122,6 +122,7 @@ typedef struct VGACommonState {
     uint32_t last_width, last_height; /* in chars or pixels */
     uint32_t last_scr_width, last_scr_height; /* in pixels */
     uint32_t last_depth; /* in bits */
+    void *last_surface;
     bool last_byteswap;
     bool force_shadow;
     uint8_t cursor_start, cursor_end;

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1784900

Title:
  QEMU (frontend) crashes upon warm reboot with virtio-gpu device and
  vga=775 on Linux cmdline

Status in QEMU:
  New

Bug description:
  With vga=775 on the Linux command line a first boot of the VM running
  Linux works fine. After a warm reboot it crashes during Linux boot.
  The VM was used remotely via virt-manager and VNC.

  Bisecting the code lead to the following patch that introduced the
  bug:

  commit 1fccd7c5a9a722a9cbf1bc91693f4618034f01ac (HEAD, refs/bisect/bad)
  Author: Gerd Hoffmann <kraxel@redhat.com>
  Date:   Mon Jul 2 18:24:43 2018 +0200

      virtio-gpu: disable scanout when backing resource is destroyed

      Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
      Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
      Message-id: 20180702162443.16796-4-kraxel@redhat.com

  diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
  index 336dc59007..08cd567218 100644
  --- a/hw/display/virtio-gpu.c
  +++ b/hw/display/virtio-gpu.c
  @@ -430,6 +430,16 @@ static void virtio_gpu_disable_scanout(VirtIOGPU *g, int scanout_id)
   static void virtio_gpu_resource_destroy(VirtIOGPU *g,
                                           struct virtio_gpu_simple_resource *res)
   {
  +    int i;
  +
  +    if (res->scanout_bitmask) {
  +        for (i = 0; i < g->conf.max_outputs; i++) {
  +            if (res->scanout_bitmask & (1 << i)) {
  +                virtio_gpu_disable_scanout(g, i);
  +            }
  +        }
  +    }
  +
       pixman_image_unref(res->image);
       virtio_gpu_cleanup_mapping(res);
       QTAILQ_REMOVE(&g->reslist, res, next);

  
  Reported backtraces can be found here:  https://paste.fedoraproject.org/paste/OUDEfCk1IY7xiy0I0PDlkw

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1784900/+subscriptions

Hi,

This series seems to have some coding style problems. See output below for
more information:

Type: series
Message-id: 153321150379.28572.4771679861864409417.malone@chaenomeles.canonical.com
Subject: [Qemu-devel] [Bug 1784900] Re: QEMU (frontend) crashes upon warm reboot with virtio-gpu device and vga=775 on Linux cmdline

=== TEST SCRIPT BEGIN ===
#!/bin/bash

BASE=base
n=1
total=$(git log --oneline $BASE.. | wc -l)
failed=0

git config --local diff.renamelimit 0
git config --local diff.renames True
git config --local diff.algorithm histogram

commits="$(git log --format=%H --reverse $BASE..)"
for c in $commits; do
    echo "Checking PATCH $n/$total: $(git log -n 1 --format=%s $c)..."
    if ! git show $c --format=email | ./scripts/checkpatch.pl --mailback -; then
        failed=1
        echo
    fi
    n=$((n+1))
done

exit $failed
=== TEST SCRIPT END ===

Updating 3c8cf5a9c21ff8782164d1def7f44bd888713384
From https://github.com/patchew-project/qemu
 * [new tag]               patchew/153321150379.28572.4771679861864409417.malone@chaenomeles.canonical.com -> patchew/153321150379.28572.4771679861864409417.malone@chaenomeles.canonical.com
Switched to a new branch 'test'
1a366fd405 QEMU (frontend) crashes upon warm reboot with virtio-gpu device and vga=775 on Linux cmdline

=== OUTPUT BEGIN ===
Checking PATCH 1/1: QEMU (frontend) crashes upon warm reboot with virtio-gpu device and vga=775 on Linux cmdline...
ERROR: line over 90 characters
#32: FILE: hw/display/vga.c:1571:
+    fprintf(stderr, "%p vs %p   share_surface: %d   surface: %p\n", surface_data(surface), s->vram_ptr + (s->start_addr * 4), share_surface, surface);

ERROR: Missing Signed-off-by: line(s)

total: 2 errors, 0 warnings, 26 lines checked

Your patch has style problems, please review.  If any of these errors
are false positives report them to the maintainer, see
CHECKPATCH in MAINTAINERS.

=== OUTPUT END ===

Test command exited with code: 1


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