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

[Oleksandr <olekstysh@xxxxxxxxx>]

On 15.12.21 04:58, Volodymyr Babchuk wrote:
> Hi Oleksandr,
Hi Volodymyr


> Oleksandr Tyshchenko <olekstysh@xxxxxxxxx> writes:
>
> > 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);
> It would be great to have
>
> +      ASSERT(mmu->utlb_refcount[utlb] > 0);
>
> there. Just in case.
ok, will add.


Thank you.


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

Oleksandr Tyshchenko