Re: [PATCH 8/8] vfio/igd: add x-igd-gms option back to set DSM region size for guest

[Corvin Köhne]

On Mon, 2024-12-02 at 00:09 +0800, Tomita Moeko wrote:
> CAUTION: External Email!!
> DSM region is likely to store framebuffer in Windows, a small DSM
> region may cause display issues (e.g. half of the screen is black).
> By default, QEMU uses host's original value, which is determined by
> DVMT Pre-Allocated option in Intel FSP of host bios. Some vendors
> do not expose this config item to users. In such cases, x-igd-gms
> option can be used to manually set the data stolen memory size for
> guest.
> 
> When DVMT Pre-Allocated option is available in host BIOS, user should
> set DSM region size there instead of using x-igd-gms option.
> 
> Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
> ---
>  hw/vfio/igd.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
> index 3fd822241d..614223123b 100644
> --- a/hw/vfio/igd.c
> +++ b/hw/vfio/igd.c
> @@ -712,6 +712,23 @@ void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int 
> nr)
>  
>      QLIST_INSERT_HEAD(&vdev->bars[nr].quirks, quirk, next);
>  
> +    /*
> +     * Allow user to override dsm size using x-igd-gms option, in multiples 
> of
> +     * 32MiB. This option should only be used when the desired size cannot be
> +     * set from DVMT Pre-Allocated option in host BIOS.
> +     */
> +    if (vdev->igd_gms) {
> +        if (gen < 8 && vdev->igd_gms <= 0x10) {
> +            gmch &= ~(IGD_GMCH_GEN6_GMS_MASK << IGD_GMCH_GEN6_GMS_SHIFT);
> +            gmch |= vdev->igd_gms << IGD_GMCH_GEN6_GMS_SHIFT;
> +        } else if (vdev->igd_gms <= 0x40) {
> +            gmch &= ~(IGD_GMCH_GEN8_GMS_MASK << IGD_GMCH_GEN8_GMS_SHIFT);
> +            gmch |= vdev->igd_gms << IGD_GMCH_GEN8_GMS_SHIFT;
> +        } else {
> +            error_report("Unsupported IGD GMS value 0x%x", vdev->igd_gms);
> +        }
> +    }
> +
>      ggms_size = igd_gtt_memory_size(gen, gmch);
>      gms_size = igd_stolen_memory_size(gen, gmch);
>  

As mentioned in my commit removing the x-igd-gms option, I've seen issues on 
Windows guest when
setting a wrong gms value. I can try to recheck this.


-- 
Kind regards,
Corvin
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