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

[Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>]

Hi Oleksandr,


Oleksandr Tyshchenko <olekstysh@gmail.com> writes:

> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>
> 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@epam.com>
> ---
>  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);

It would be great to have

+      ASSERT(mmu->utlb_refcount[utlb] > 0);

there. Just in case.

> +    if ( --mmu->utlb_refcount[utlb] == 0 )
> +        ipmmu_imuctr_write(mmu, utlb, 0);
>  }
>  
>  /* Domain/Context Management */


-- 
Volodymyr Babchuk at EPAM