RE: [PATCH 09/10] iommu/ipmmu-vmsa: Use refcount for the micro-TLBs

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>]

Hello Oleksandr-san,

Thank you for the patch!

> From: Oleksandr Tyshchenko, Sent: Sunday, November 28, 2021 2:52 AM
> 
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> 
> Reference-count the micro-TLBs as several bus masters can be
> connected to the same micro-TLB (and drop TODO comment).
> This wasn't an issue so far, since the platform devices
> (this driver deals with) get assigned/deassigned together during
> domain creation/destruction. But, in order to support PCI devices
> (which are hot-pluggable) in the near future we will need to
> take care of.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> ---
>  xen/drivers/passthrough/arm/ipmmu-vmsa.c | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/xen/drivers/passthrough/arm/ipmmu-vmsa.c 
> b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
> index 22dd84e..32609f8 100644
> --- a/xen/drivers/passthrough/arm/ipmmu-vmsa.c
> +++ b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
> @@ -134,6 +134,7 @@ struct ipmmu_vmsa_device {
>      spinlock_t lock;    /* Protects ctx and domains[] */
>      DECLARE_BITMAP(ctx, IPMMU_CTX_MAX);
>      struct ipmmu_vmsa_domain *domains[IPMMU_CTX_MAX];
> +    unsigned int utlb_refcount[IPMMU_UTLB_MAX];
>      const struct ipmmu_features *features;
>  };
> 
> @@ -477,13 +478,12 @@ static int ipmmu_utlb_enable(struct ipmmu_vmsa_domain 
> *domain,
>          }
>      }
> 
> -    /*
> -     * TODO: Reference-count the micro-TLB as several bus masters can be
> -     * connected to the same micro-TLB.
> -     */
> -    ipmmu_imuasid_write(mmu, utlb, 0);
> -    ipmmu_imuctr_write(mmu, utlb, imuctr |
> -                       IMUCTR_TTSEL_MMU(domain->context_id) | IMUCTR_MMUEN);
> +    if ( mmu->utlb_refcount[utlb]++ == 0 )
> +    {
> +        ipmmu_imuasid_write(mmu, utlb, 0);
> +        ipmmu_imuctr_write(mmu, utlb, imuctr |
> +                           IMUCTR_TTSEL_MMU(domain->context_id) | 
> IMUCTR_MMUEN);
> +    }
> 
>      return 0;
>  }
> @@ -494,7 +494,8 @@ static void ipmmu_utlb_disable(struct ipmmu_vmsa_domain 
> *domain,
>  {
>      struct ipmmu_vmsa_device *mmu = domain->mmu;
> 
> -    ipmmu_imuctr_write(mmu, utlb, 0);

As Volodymyr-san mentioned before, after we added ASSERT(),

Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>

Best regards,
Yoshihiro Shimoda