Re: [PATCH v2 1/3] stdvga: fix screen blanking

[Marc-André Lureau <marcandre.lureau@xxxxxxxxxx>]

Hi

On Mon, Jun 3, 2024 at 7:18 PM Gerd Hoffmann <kraxel@xxxxxxxxxx> wrote:
>
> In case the display surface uses a shared buffer (i.e. uses vga vram
> directly instead of a shadow) go unshare the buffer before clearing it.
>
> This avoids vga memory corruption, which in turn fixes unblanking not
> working properly with X11.
>
> Cc: qemu-stable@xxxxxxxxxx
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2067
> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> ---
>  hw/display/vga.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/hw/display/vga.c b/hw/display/vga.c
> index 30facc6c8e33..474b6b14c327 100644
> --- a/hw/display/vga.c
> +++ b/hw/display/vga.c
> @@ -1762,6 +1762,12 @@ static void vga_draw_blank(VGACommonState *s, int 
> full_update)
>      if (s->last_scr_width <= 0 || s->last_scr_height <= 0)
>          return;
>
> +    if (is_buffer_shared(surface)) {

Perhaps the suggestion to rename the function (in the following patch)
should instead be surface_is_allocated() ? that would match the actual
flag check. But callers would have to ! the result. Wdyt?

> +        /* unshare buffer, otherwise the blanking corrupts vga vram */
> +        surface = qemu_create_displaysurface(s->last_scr_width, 
> s->last_scr_height);
> +        dpy_gfx_replace_surface(s->con, surface);

Ok, this looks safer than calling "resize".

thanks

> +    }
> +
>      w = s->last_scr_width * surface_bytes_per_pixel(surface);
>      d = surface_data(surface);
>      for(i = 0; i < s->last_scr_height; i++) {
> --
> 2.45.1
>