Re: [PATCH v3 03/10] vfio/igd: fix GTT stolen memory size calculation for gen 8+

[Alex Williamson]

On Thu,  5 Dec 2024 18:55:28 +0800
Tomita Moeko <tomitamoeko@gmail.com> wrote:

> On gen 8 and later devices, the GTT stolen memory size when GGMS equals
> 0 is 0 (no preallocated memory) rather than 1MB [1].
> 
> [1] 3.1.13, 5th Generation Intel Core Processor Family Datasheet Vol. 2
>     https://www.intel.com/content/www/us/en/content-details/330835
> 
> Reported-By: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
> ---
>  hw/vfio/igd.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

This should come before the preceding patch in the series so that we're
not making a fix dependent on other code churn.  This makes it easier
to backport to stable branches.  Also we should include the tag:

Fixes: c4c45e943e51 ("vfio/pci: Intel graphics legacy mode assignment")

Otherwise the series looks good now.  Thanks,

Alex

> diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
> index 18d179bc83..09bd4e5383 100644
> --- a/hw/vfio/igd.c
> +++ b/hw/vfio/igd.c
> @@ -259,7 +259,7 @@ static int vfio_igd_gtt_max(VFIOPCIDevice *vdev)
>  
>      gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH, sizeof(gmch));
>      ggms = (gmch >> (gen < 8 ? 8 : 6)) & 0x3;
> -    if (gen >= 8) {
> +    if (gen >= 8 && ggms != 0) {
>          ggms = 1 << ggms;
>      }
>  
> @@ -669,7 +669,7 @@ void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int 
> nr)
>  
>      /* Determine the size of stolen memory needed for GTT */
>      ggms_mb = (gmch >> (gen < 8 ? 8 : 6)) & 0x3;
> -    if (gen >= 8) {
> +    if (gen >= 8 && ggms_mb != 0) {
>          ggms_mb = 1 << ggms_mb;
>      }
>