Re: [PATCH 10/11] vfio/igd: Remove generation limitation for IGD passthrough

["Corvin Köhne" <C.Koehne@beckhoff.com>]

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On Tue, 2025-04-22 at 00:31 +0800, Tomita Moeko wrote:
> CAUTION: External Email!!
> Starting from Intel Core Ultra Series (Meteor Lake), Data Stolen Memory
> has became a part of LMEMBAR (MMIO BAR2) [1][2], meaning that BDSM and
> GGC register quirks are no longer needed on these platforms.
> 
> To support Meteor/Arrow/Lunar Lake and future IGD devices, remove the
> generation limitation in IGD passthrough, and apply BDSM and GGC quirks
> only to known Gen6-12 devices.
> 
> [1]
> https://nospamproxywebp.beckhoff.com/enQsig/link?id=BAgAAABHhgBhwX01GO0AAACNi-GgHiUI4sV0qRTHkaBvP5PrY5DqqTz9YhuTNO_iXQUZlCVu442aEFUtFJIN9H4QuJJwNJh5ry3XO19WptfEahlpGX9F7Nq8Xpv-GQ9_LZd6niU0I-kMcs9DxxlKk8E802ILvUeF86QyZP4D7A7AEaoUDo15UvzlwHlTOoUj4fzKJYvykniL_MlVr8H8FS2ySMcVqfE6IFb5Aiwhkq7hrpL53XHUYCVoK_y89PCzSWC-Y0fS5-Xo-SxRDOtI140aTd7KpmA39tf447LtBR1YQP8ccM8PjukqvroMpZtV3cDQcgya3EsmP0Fgrmc1
>  
> [2]
> https://nospamproxywebp.beckhoff.com/enQsig/link?id=BAgAAABHhgBhwX01GNYAAAAtMYPOda9hw4SLBezXYKaYHKRl05pN8tzXcVl9njzCJlE1HkXUG-mljVszTJQKhcQYQTJNcuCekCys_GWgxsVTyOaS_NHFmHSUCZG_K4lK67xtRF6gmeuH6VTzSH0evGV976t_N2r5ADGfofxEA3bNt0iJmL1IzjhRilkRiNe-EmvdQ7DLMn1nAV9ZQCkPM5bCjIyd7MIjXMAlwhK4CraFMv1xw33w-ZnR0YrP4VIGHwKE7vUKp7-BjGZzyrgtwQ5m2SKD0zkEOs3dls5l351dSvNfqp740
>  
> 
> Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
> ---
>  hw/vfio/igd.c | 58 +++++++++++++++++++--------------------------------
>  1 file changed, 21 insertions(+), 37 deletions(-)
> 
> diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
> index bc4c79837d..5b888616f0 100644
> --- a/hw/vfio/igd.c
> +++ b/hw/vfio/igd.c
> @@ -103,6 +103,7 @@ static int igd_gen(VFIOPCIDevice *vdev)
>      /*
>       * Unfortunately, Intel changes it's specification quite often. This
> makes
>       * it impossible to use a suitable default value for unknown devices.
> +     * Return -1 for not applying any generation-specific quirks.
>       */
>      return -1;
>  }
> @@ -434,20 +435,12 @@ void vfio_probe_igd_bar0_quirk(VFIOPCIDevice *vdev, int
> nr)
>      VFIOConfigMirrorQuirk *ggc_mirror, *bdsm_mirror;
>      int gen;
>  
> -    /*
> -     * This must be an Intel VGA device at address 00:02.0 for us to even
> -     * consider enabling legacy mode. Some driver have dependencies on the
> PCI
> -     * bus address.
> -     */

Same goes for this comment. It's not really correct as UEFI GOP and OS driver
depend on address 0:2.0 too but I'd keep and improve it to make it more clear
for future reader.

>      if (!vfio_pci_is(vdev, PCI_VENDOR_ID_INTEL, PCI_ANY_ID) ||
>          !vfio_is_vga(vdev) || nr != 0) {
>          return;
>      }
>  
> -    /*
> -     * Only on IGD devices of gen 11 and above, the BDSM register is mirrored
> -     * into MMIO space and read from MMIO space by the Windows driver.
> -     */
> +    /* Only on IGD Gen6-12 device needs quirks in BAR 0 */
>      gen = igd_gen(vdev);
>      if (gen < 6) {
>          return;
> @@ -494,7 +487,7 @@ static bool vfio_pci_igd_config_quirk(VFIOPCIDevice *vdev,
> Error **errp)
>  {
>      g_autofree struct vfio_region_info *opregion = NULL;
>      int ret, gen;
> -    uint64_t gms_size;
> +    uint64_t gms_size = 0;
>      uint64_t *bdsm_size;
>      uint32_t gmch;
>      bool legacy_mode_enabled = false;
> @@ -514,18 +507,7 @@ static bool vfio_pci_igd_config_quirk(VFIOPCIDevice
> *vdev, Error **errp)
>      }
>      info_report("OpRegion detected on Intel display %x.", vdev->device_id);
>  
> -    /*
> -     * IGD is not a standard, they like to change their specs often.  We
> -     * only attempt to support back to SandBridge and we hope that newer
> -     * devices maintain compatibility with generation 8.
> -     */
>      gen = igd_gen(vdev);
> -    if (gen == -1) {
> -        error_report("IGD device %s is unsupported in legacy mode, "
> -                     "try SandyBridge or newer", vdev-
> >https://nospamproxywebp.beckhoff.com/enQsig/link?id=BAgAAABHhgBhwX01GGwAAADNE
> nn7fAHvEAN3EJV6Ng4dOzKc7MR7f3e317FXOTfRW-ZxuzGFRyquEjUjSeP-
> 6ByDI2TtwvI3jwlJBjQdXL-V9t40AFbX3wSV_K-
> M0j4dDCcdYxjOhLKhEroDvVJ0XE20BM2QEteRk67iEFo1 );
> -        return true;
> -    }
> -
>      gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH, 4);
>  
>      /*
> @@ -624,32 +606,34 @@ static bool vfio_pci_igd_config_quirk(VFIOPCIDevice
> *vdev, Error **errp)
>          }
>      }
>  
> -    gms_size = igd_stolen_memory_size(gen, gmch);
> +    if (gen > 0) {
> +        gms_size = igd_stolen_memory_size(gen, gmch);
> +
> +        /* BDSM is read-write, emulated. BIOS needs to be able to write it */
> +        if (gen < 11) {
> +            pci_set_long(vdev->pdev.config + IGD_BDSM, 0);
> +            pci_set_long(vdev->pdev.wmask + IGD_BDSM, ~0);
> +            pci_set_long(vdev->emulated_config_bits + IGD_BDSM, ~0);
> +        } else {
> +            pci_set_quad(vdev->pdev.config + IGD_BDSM_GEN11, 0);
> +            pci_set_quad(vdev->pdev.wmask + IGD_BDSM_GEN11, ~0);
> +            pci_set_quad(vdev->emulated_config_bits + IGD_BDSM_GEN11, ~0);
> +        }
> +    }
>  
>      /*
>       * Request reserved memory for stolen memory via fw_cfg.  VM firmware
>       * must allocate a 1MB aligned reserved memory region below 4GB with
> -     * the requested size (in bytes) for use by the Intel PCI class VGA
> -     * device at VM address 00:02.0.  The base address of this reserved
> -     * memory region must be written to the device BDSM register at PCI
> -     * config offset 0x5C.
> +     * the requested size (in bytes) for use by the IGD device. The base
> +     * address of this reserved memory region must be written to the
> +     * device BDSM register.
> +     * For newer device without BDSM register, this fw_cfg item is 0.
>       */
>      bdsm_size = g_malloc(sizeof(*bdsm_size));
>      *bdsm_size = cpu_to_le64(gms_size);
>      fw_cfg_add_file(fw_cfg_find(), "etc/igd-bdsm-size",
>                      bdsm_size, sizeof(*bdsm_size));
>  
> -    /* BDSM is read-write, emulated.  The BIOS needs to be able to write it
> */
> -    if (gen < 11) {
> -        pci_set_long(vdev->pdev.config + IGD_BDSM, 0);
> -        pci_set_long(vdev->pdev.wmask + IGD_BDSM, ~0);
> -        pci_set_long(vdev->emulated_config_bits + IGD_BDSM, ~0);
> -    } else {
> -        pci_set_quad(vdev->pdev.config + IGD_BDSM_GEN11, 0);
> -        pci_set_quad(vdev->pdev.wmask + IGD_BDSM_GEN11, ~0);
> -        pci_set_quad(vdev->emulated_config_bits + IGD_BDSM_GEN11, ~0);
> -    }
> -
>      trace_vfio_pci_igd_bdsm_enabled(vdev-
> >https://nospamproxywebp.beckhoff.com/enQsig/link?id=BAgAAABHhgBhwX01GGwAAADNE
> nn7fAHvEAN3EJV6Ng4dOzKc7MR7f3e317FXOTfRW-ZxuzGFRyquEjUjSeP-
> 6ByDI2TtwvI3jwlJBjQdXL-V9t40AFbX3wSV_K-
> M0j4dDCcdYxjOhLKhEroDvVJ0XE20BM2QEteRk67iEFo1 , (gms_size / MiB));
>  
>      return true;

-- 
Kind regards,
Corvin

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