Re: [PATCH v4 09/19] hw/arm/smmu-common: Rework TLB lookup for nesting

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

On Mon, Jul 01, 2024 at 11:02:31AM +0000, Mostafa Saleh wrote:
> In the next patch, combine_tlb() will be added which combines 2 TLB
> entries into one for nested translations, which chooses the granule
> and level from the smallest entry.
> 
> This means that with nested translation, an entry can be cached with
> the granule of stage-2 and not stage-1.
> 
> However, currently, the lookup for an IOVA is done with input stage
> granule, which is stage-1 for nested configuration, which will not
> work with the above logic.
> This patch reworks lookup in that case, so it falls back to stage-2
> granule if no entry is found using stage-1 granule.

Why not initialize tt_combined to the minimum granule of stages 1 and 2?
It looks like you introduced it for this. I'm wondering if we lookup the
wrong IOVA if changing the granule size after the address is masked in
smmu_translate()

Thanks,
Jean

> 
> Signed-off-by: Mostafa Saleh <smostafa@google.com>
> ---
>  hw/arm/smmu-common.c | 36 ++++++++++++++++++++++++++++++++++--
>  1 file changed, 34 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/arm/smmu-common.c b/hw/arm/smmu-common.c
> index 21982621c0..0840b5cffd 100644
> --- a/hw/arm/smmu-common.c
> +++ b/hw/arm/smmu-common.c
> @@ -66,8 +66,10 @@ SMMUIOTLBKey smmu_get_iotlb_key(int asid, int vmid, uint64_t iova,
>      return key;
>  }
>  
> -SMMUTLBEntry *smmu_iotlb_lookup(SMMUState *bs, SMMUTransCfg *cfg,
> -                                SMMUTransTableInfo *tt, hwaddr iova)
> +static SMMUTLBEntry *smmu_iotlb_lookup_all_levels(SMMUState *bs,
> +                                                  SMMUTransCfg *cfg,
> +                                                  SMMUTransTableInfo *tt,
> +                                                  hwaddr iova)
>  {
>      uint8_t tg = (tt->granule_sz - 10) / 2;
>      uint8_t inputsize = 64 - tt->tsz;
> @@ -88,6 +90,36 @@ SMMUTLBEntry *smmu_iotlb_lookup(SMMUState *bs, SMMUTransCfg *cfg,
>          }
>          level++;
>      }
> +    return entry;
> +}
> +
> +/**
> + * smmu_iotlb_lookup - Look up for a TLB entry.
> + * @bs: SMMU state which includes the TLB instance
> + * @cfg: Configuration of the translation
> + * @tt: Translation table info (granule and tsz)
> + * @iova: IOVA address to lookup
> + *
> + * returns a valid entry on success, otherwise NULL.
> + * In case of nested translation, tt can be updated to include
> + * the granule of the found entry as it might different from
> + * the IOVA granule.
> + */
> +SMMUTLBEntry *smmu_iotlb_lookup(SMMUState *bs, SMMUTransCfg *cfg,
> +                                SMMUTransTableInfo *tt, hwaddr iova)
> +{
> +    SMMUTLBEntry *entry = NULL;
> +
> +    entry = smmu_iotlb_lookup_all_levels(bs, cfg, tt, iova);
> +    /*
> +     * For nested translation also try the s2 granule, as the TLB will insert
> +     * it if the size of s2 tlb entry was smaller.
> +     */
> +    if (!entry && (cfg->stage == SMMU_NESTED) &&
> +        (cfg->s2cfg.granule_sz != tt->granule_sz)) {
> +        tt->granule_sz = cfg->s2cfg.granule_sz;
> +        entry = smmu_iotlb_lookup_all_levels(bs, cfg, tt, iova);
> +    }
>  
>      if (entry) {
>          cfg->iotlb_hits++;
> -- 
> 2.45.2.803.g4e1b14247a-goog
>