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

[Tomita Moeko]

On 12/2/24 13:28, Alex Williamson wrote:
> 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
>> +
>> +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.

Got it, will fix in v2

>> +    } 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.

It was changed to return size in bytes, instead of size in MB, to make
the behavior of 2 size calculation functions consistent. Original one
should be changed to.
        return ((gms - 0xf0) * 4 + 4) * MiB;
Then I changed it to
        return (gms - 0xf0 + 1) * 4 * MiB;
to make it easier to read. gms is uint64, the masked value is 0xff at
most, +1 won't cause overflow here.

>> +        }
>> +    }
>> +
>> +    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->vbasedev.name);
>>      }
>>  
>> -    trace_vfio_pci_igd_bdsm_enabled(vdev->vbasedev.name, ggms_mb + gms_mb);
>> +    trace_vfio_pci_igd_bdsm_enabled(vdev->vbasedev.name, *bdsm_size / MiB);
> 
> Technically this should use le64_to_cpu(*bdsm_size), or retain the
> addition logic.  Thanks,

Got it.

> Alex
>