Re: [PATCH qemu-server v4 1/3] fix #6277: virtio-vga-gl: add OpenGL 4.6 and Vulkan (Venus) support

[Dominik Csapak <d.csapak@proxmox.com>]

answering for markus now because i looked this up

On 8/31/26 5:44 PM, DERUMIER, Alexandre wrote:
> also,
> 
> I think it's missing the memory backend
> 
> -object memory-backend-memfd,id=mem1,size=2G
> -machine memory-backend=mem1
> 
> (or maybe virgl-server avoid it ?)

for virtio-vga-gl,blob=on,venus=on no memory backend is needed.
this is only needed when turning on blob=on on a 'regular' virtio-gpu 
device (non-gl)

for virtio-vga-gl, the virgl-server allocates the memory...

> 
> 
> 
> Le lundi 31 août 2026 à 11:38 +0200, Markus Frank a écrit :
>> Adding the 'blob=on,hostmem=<size>' parameters to the 'virtio-gpu-gl'
>> device allows the VM to use OpenGL 4.6. By default virtio-gpu-gl only
>> supports up to OpenGL 4.3.
>>
>> If Vulkan support is needed, the 'venus=on' parameter is added to the
>> 'virtio-gpu-gl' device, in addition to the two parameters required
>> for
>> OpenGL 4.6.
>>
>> The Venus protocol facilitates the translation of Vulkan API calls
>> via
>> the virglrenderer. To use it, the virgl-server package must be
>> installed
>> on the host.
>>
>> Set the default VirGL memory window to 2048 MiB, as having less could
>> lead to instability inside the VM.
>>
>> Signed-off-by: Markus Frank <m.frank@proxmox.com>
>> ---
>> v4:
>> * made the description of virgl-features more general
>> * added bugzilla number to commit message
>>
>>   src/PVE/QemuServer.pm | 36 +++++++++++++++++++++++++++++++++++-
>>   1 file changed, 35 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/PVE/QemuServer.pm b/src/PVE/QemuServer.pm
>> index 63d8c135..65c4a804 100644
>> --- a/src/PVE/QemuServer.pm
>> +++ b/src/PVE/QemuServer.pm
>> @@ -171,6 +171,20 @@ my $vga_fmt = {
>>               qw(cirrus qxl qxl2 qxl3 qxl4 none serial0 serial1
>> serial2 serial3 std virtio virtio-gl vmware)
>>           ],
>>       },
>> +    'virgl-features' => {
>> +        description => 'Enable additional features on VirGL GPU.',
>> +        type => 'string',
>> +        optional => 1,
>> +        enum => ['opengl4.6', 'opengl4.6+vulkan'],
>> +    },
>> +    'virgl-memory-window' => {
>> +        description => 'Set the VirGL host memory window. This
>> option allocates'
>> +            . ' host memory to act as VRAM in the VM.',
>> +        type => 'string',
>> +        default => '2048',
>> +        optional => 1,
>> +        enum => ['512', '1024', '2048', '4096', '8192'],
>> +    },
>>       memory => {
>>           description => "Sets the VGA memory (in MiB). Has no effect
>> with serial display.",
>>           type => 'integer',
>> @@ -1549,6 +1563,23 @@ sub print_vga_device {
>>           $pciaddr = print_pci_addr($vgaid, $bridges, $arch);
>>       }
>>   
>> +    my $virgl_param = "";
>> +    my $virgl_mode = $vga->{'virgl-features'};
>> +    if ($virgl_mode) {
>> +        my $virgl_memory_window = $vga->{'virgl-memory-window'}
>> +            // $vga_fmt->{'virgl-memory-window'}->{'default'};
>> +        $virgl_param = ",hostmem=${virgl_memory_window}M,blob=on";
>> +
>> +        if ($virgl_mode eq 'opengl4.6+vulkan') {
>> +            $virgl_param .= ",venus=on";
>> +            log_warn(
>> +                "missing virgl render server for Vulkan (Venus)
>> support! Please install 'virgl-server'.\n"
>> +            ) if !-e "/usr/libexec/virgl_render_server";
>> +        }
>> +    } elsif ($vga->{'virgl-memory-window'}) {
>> +        die "To use a VirGL host memory window, please select a
>> compatible VirGL feature set.\n";
>> +    }
>> +
>>       if ($vga->{type} eq 'virtio-gl') {
>>           # VirGL renders on the host, so the guest arch is irrelevant
>> for the library lookup
>>           my $host_arch = get_host_arch();
>> @@ -1560,9 +1591,12 @@ sub print_vga_device {
>>           die
>>               "no DRM render node detected (/dev/dri/renderD*), no
>> GPU? - needed for '$vga->{type}' display\n"
>>               if !PVE::Tools::dir_glob_regex('/dev/dri/',
>> "renderD.*");
>> +
>> +    } elsif ($virgl_mode) {
>> +        die "You need to use virtio-gl to enable OpenGL 4.6 or
>> Vulkan support!\n";
>>       }
>>   
>> -    return
>> "$type,id=${vgaid}${memory}${max_outputs}${pciaddr}${edidoff}";
>> +    return
>> "$type,id=${vgaid}${memory}${max_outputs}${pciaddr}${edidoff}${virgl_
>> param}";
>>   }
>>   
>>   sub vm_is_volid_owner {