Re: [Qemu-devel] [PATCH] cirrus_vga: adding sanity check for vram size

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* arei.gonglei@huawei.com (arei.gonglei@huawei.com) wrote:
> From: Gonglei <arei.gonglei@huawei.com>
> 
> when configure a invalid vram size for cirrus card, such as less
> 2 MB, which will crash qemu. Follow the real hardware, the cirrus
> card has 4 MB video memory. Also for backward compatibility, accept
> 8 MB and 16 MB vram size.

virt-manager/libvirt seems to default to 9 MByte of Vram for cirrus,
so this would break a lot of setups.

Looking at datasheets on the web seems to say the chips actually went
down to 1 MB or less.

I think before doing this change, it would be good to understand where
the weird 9MB in libvirt/virt-manager came from, and what the limits of
the emulator/drivers are.

Also, is there something broken at the moment - why make the change?

Dave

> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
> For isa cirrus vga device, its' init function has been droped at
> commit db895a1e6a97e919f9b86d60c969377357b05066. I have no idea how adding
> check on isa_cirrus_vga device. Any ideas? Thanks.
>  
>  hw/display/cirrus_vga.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
> index d1afc76..5fec068 100644
> --- a/hw/display/cirrus_vga.c
> +++ b/hw/display/cirrus_vga.c
> @@ -2959,6 +2959,13 @@ static int pci_cirrus_vga_initfn(PCIDevice *dev)
>       PCIDeviceClass *pc = PCI_DEVICE_GET_CLASS(dev);
>       int16_t device_id = pc->device_id;
>  
> +     /* follow real hardware, cirrus card emulated has 4 MB video memory.
> +       Also accept 8 MB/16 MB for backward compatibility. */
> +     if (s->vga.vram_size_mb != 4 || s->vga.vram_size_mb != 8 ||
> +         s->vga.vram_size_mb != 16) {
> +         error_report("Invalid cirrus_vga ram size '%u'\n", s->vga.vram_size_mb);
> +         return -1;
> +     }
>       /* setup VGA */
>       vga_common_init(&s->vga, OBJECT(dev), true);
>       cirrus_init_common(s, OBJECT(dev), device_id, 1, pci_address_space(dev),
> -- 
> 1.7.12.4
> 
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK