Re: [PATCH 2/8] vfio/igd: canonicalize memory size calculations

[Corvin Köhne]

On Sun, 2024-12-01 at 22:28 -0700, Alex Williamson wrote:
> CAUTION: External Email!!
> On Mon,  2 Dec 2024 00:09:32 +0800
> Tomita Moeko <tomitamoeko@gmail.com> wrote:
> 
> > Add helper functions igd_gtt_memory_size() and igd_stolen_size() for
> > calculating GTT stolen memory and Data stolen memory size in bytes,
> > and use macros to replace the hardware-related magic numbers for
> > better readability.
> > 
> > Signed-off-by: Tomita Moeko <tomitamoeko@gmail.com>
> > ---
> >  hw/vfio/igd.c | 101 ++++++++++++++++++++++++++++-------------------
> > ---
> >  1 file changed, 57 insertions(+), 44 deletions(-)
> > 
> > diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
> > index e40e601026..b449316ec0 100644
> > --- a/hw/vfio/igd.c
> > +++ b/hw/vfio/igd.c
> > @@ -116,6 +116,54 @@ typedef struct VFIOIGDQuirk {
> >  #define IGD_BDSM 0x5c /* Base Data of Stolen Memory */
> >  #define IGD_BDSM_GEN11 0xc0 /* Base Data of Stolen Memory of gen 11
> > and later */
> >  
> > +#define IGD_GMCH_GEN6_GMS_SHIFT     3
> > +#define IGD_GMCH_GEN6_GMS_MASK      0x1f
> > +#define IGD_GMCH_GEN6_GGMS_SHIFT    8
> > +#define IGD_GMCH_GEN6_GGMS_MASK     0x3
> > +#define IGD_GMCH_GEN8_GMS_SHIFT     8
> > +#define IGD_GMCH_GEN8_GMS_MASK      0xff
> > +#define IGD_GMCH_GEN8_GGMS_SHIFT    6
> > +#define IGD_GMCH_GEN8_GGMS_MASK     0x3
> > +

You should consider reusing the names used by Linux [1].

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/drm/intel/i915_drm.h?h=v6.12#n50

> > +static uint64_t igd_gtt_memory_size(int gen, uint16_t gmch)
> > +{
> > +    uint64_t ggms;
> > +
> > +    if (gen < 8) {
> > +        ggms = (gmch >> IGD_GMCH_GEN6_GGMS_SHIFT) &
> > IGD_GMCH_GEN6_GGMS_MASK;
> > +    } else {
> > +        ggms = (gmch >> IGD_GMCH_GEN8_GGMS_SHIFT) &
> > IGD_GMCH_GEN8_GGMS_MASK;
> > +        ggms *= 2;
> > +    }
> > +
> > +    return ggms * MiB;
> > +}
> > +
> > +static uint64_t igd_stolen_memory_size(int gen, uint32_t gmch)
> > +{
> > +    uint64_t gms;
> > +
> > +    if (gen < 8) {
> > +        gms = (gmch >> IGD_GMCH_GEN6_GMS_SHIFT) &
> > IGD_GMCH_GEN6_GMS_MASK;
> > +    } else {
> > +        gms = (gmch >> IGD_GMCH_GEN8_GMS_SHIFT) &
> > IGD_GMCH_GEN8_GMS_MASK;
> > +    }
> > +
> > +    if (gen < 9) {
> > +        if (gms < 0x10) {
> > +            return gms * 32 * MiB;
> > +        }
> 
> igd_get_stolen_mb() used:
> 
>         if (gms > 0x10) {
>             error_report("Unsupported IGD GMS value 0x%x", gms);
>             return 0;
>         }
>         return gms * 32;
> 
> Therefore this should use <= to be equivalent.

I'd personally prefer moving the code in one commit and change the
format in a second one.

If you want to touch this, I'd align it with Linux, which multiplies gms
by 32 MB unconditionally for gen 6 and 8 [1].

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/early-quirks.c?h=v6.12#n404

> > +    } else {
> > +        if (gms < 0xf0) {
> > +            return gms * 32 * MiB;
> > +        } else {
> > +            return (gms - 0xf0 + 1) * 4 * MiB;
> 
> This does not match the line from igd_get_stolen_mb():
> 
>             return (gms - 0xf0) * 4 + 4;
> 
> Explain.
> 

I've chosen the current format because it aligns with Linux [1]. I would
keep it as is to make it easier to sync with Linux.

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/early-quirks.c?h=v6.12#n460

> > +        }
> > +    }
> > +
> > +    error_report("Unsupported IGD GMS value 0x%lx", gms);
> > +    return 0;
> > +}
> >  
> >  /*
> >   * The rather short list of registers that we copy from the host
> > devices.
> > @@ -264,17 +312,10 @@ static int vfio_pci_igd_lpc_init(VFIOPCIDevice
> > *vdev,
> >  static int vfio_igd_gtt_max(VFIOPCIDevice *vdev)
> >  {
> >      uint32_t gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH,
> > sizeof(gmch));
> > -    int ggms, gen = igd_gen(vdev);
> > -
> > -    gmch = vfio_pci_read_config(&vdev->pdev, IGD_GMCH,
> > sizeof(gmch));
> > -    ggms = (gmch >> (gen < 8 ? 8 : 6)) & 0x3;
> > -    if (gen > 7) {
> > -        ggms = 1 << ggms;
> > -    }
> > -
> > -    ggms *= MiB;
> > +    int gen = igd_gen(vdev);
> > +    uint64_t ggms_size = igd_gtt_memory_size(gen, gmch);
> >  
> > -    return (ggms / (4 * KiB)) * (gen < 8 ? 4 : 8);
> > +    return (ggms_size / (4 * KiB)) * (gen < 8 ? 4 : 8);
> >  }
> >  
> >  /*
> > @@ -481,30 +522,6 @@ void vfio_probe_igd_bar0_quirk(VFIOPCIDevice
> > *vdev, int nr)
> >      QLIST_INSERT_HEAD(&vdev->bars[nr].quirks, quirk, next);
> >  }
> >  
> > -static int igd_get_stolen_mb(int gen, uint32_t gmch)
> > -{
> > -    int gms;
> > -
> > -    if (gen < 8) {
> > -        gms = (gmch >> 3) & 0x1f;
> > -    } else {
> > -        gms = (gmch >> 8) & 0xff;
> > -    }
> > -
> > -    if (gen < 9) {
> > -        if (gms > 0x10) {
> > -            error_report("Unsupported IGD GMS value 0x%x", gms);
> > -            return 0;
> > -        }
> > -        return gms * 32;
> > -    } else {
> > -        if (gms < 0xf0)
> > -            return gms * 32;
> > -        else
> > -            return (gms - 0xf0) * 4 + 4;
> > -    }
> > -}
> > -
> >  void vfio_probe_igd_bar4_quirk(VFIOPCIDevice *vdev, int nr)
> >  {
> >      g_autofree struct vfio_region_info *rom = NULL;
> > @@ -514,7 +531,8 @@ void vfio_probe_igd_bar4_quirk(VFIOPCIDevice
> > *vdev, int nr)
> >      VFIOQuirk *quirk;
> >      VFIOIGDQuirk *igd;
> >      PCIDevice *lpc_bridge;
> > -    int i, ret, ggms_mb, gms_mb = 0, gen;
> > +    int i, ret, gen;
> > +    uint64_t ggms_size, gms_size;
> >      uint64_t *bdsm_size;
> >      uint32_t gmch;
> >      uint16_t cmd_orig, cmd;
> > @@ -676,13 +694,8 @@ void vfio_probe_igd_bar4_quirk(VFIOPCIDevice
> > *vdev, int nr)
> >  
> >      QLIST_INSERT_HEAD(&vdev->bars[nr].quirks, quirk, next);
> >  
> > -    /* Determine the size of stolen memory needed for GTT */
> > -    ggms_mb = (gmch >> (gen < 8 ? 8 : 6)) & 0x3;
> > -    if (gen > 7) {
> > -        ggms_mb = 1 << ggms_mb;
> > -    }
> > -
> > -    gms_mb = igd_get_stolen_mb(gen, gmch);
> > +    ggms_size = igd_gtt_memory_size(gen, gmch);
> > +    gms_size = igd_stolen_memory_size(gen, gmch);
> >  
> >      /*
> >       * Request reserved memory for stolen memory via fw_cfg.  VM
> > firmware
> > @@ -693,7 +706,7 @@ void vfio_probe_igd_bar4_quirk(VFIOPCIDevice
> > *vdev, int nr)
> >       * config offset 0x5C.
> >       */
> >      bdsm_size = g_malloc(sizeof(*bdsm_size));
> > -    *bdsm_size = cpu_to_le64((ggms_mb + gms_mb) * MiB);
> > +    *bdsm_size = cpu_to_le64(ggms_size + gms_size);
> >      fw_cfg_add_file(fw_cfg_find(), "etc/igd-bdsm-size",
> >                      bdsm_size, sizeof(*bdsm_size));
> >  
> > @@ -744,5 +757,5 @@ void vfio_probe_igd_bar4_quirk(VFIOPCIDevice
> > *vdev, int nr)
> >                       vdev-
> > >https://nospamproxywebp.beckhoff.com/enQsig/link?id=BAgAAAD3YuKN4_e
> > If2wAAADsWKVxcuZtvheRgRqIemuzgT-OABVjIqlMqKN-
> > EU30bxV28qXZ_Y5_SMs0YfH8q_KtHOPLp1QG1mJuzWERjIVCEePSftEKzXou_Qr3jboY
> > Ii_VUdvptqZTIPyfY-GJ9iOrnUrKoc_oifOB9wY1 );
> >      }
> >  
> > -    trace_vfio_pci_igd_bdsm_enabled(vdev-
> > >https://nospamproxywebp.beckhoff.com/enQsig/link?id=BAgAAAD3YuKN4_e
> > If2wAAADsWKVxcuZtvheRgRqIemuzgT-OABVjIqlMqKN-
> > EU30bxV28qXZ_Y5_SMs0YfH8q_KtHOPLp1QG1mJuzWERjIVCEePSftEKzXou_Qr3jboY
> > Ii_VUdvptqZTIPyfY-GJ9iOrnUrKoc_oifOB9wY1 , ggms_mb + gms_mb);
> > +    trace_vfio_pci_igd_bdsm_enabled(vdev-
> > >https://nospamproxywebp.beckhoff.com/enQsig/link?id=BAgAAAD3YuKN4_e
> > If2wAAADsWKVxcuZtvheRgRqIemuzgT-OABVjIqlMqKN-
> > EU30bxV28qXZ_Y5_SMs0YfH8q_KtHOPLp1QG1mJuzWERjIVCEePSftEKzXou_Qr3jboY
> > Ii_VUdvptqZTIPyfY-GJ9iOrnUrKoc_oifOB9wY1 , *bdsm_size / MiB);
> 
> Technically this should use le64_to_cpu(*bdsm_size), or retain the
> addition logic.  Thanks,
> 
> Alex

-- 
Kind regards,
Corvin
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