Re: [PATCH V2 09/10] iommu/ipmmu-vmsa: Use refcount for the micro-TLBs

[Oleksandr <olekstysh@xxxxxxxxx>]

On 27.01.22 13:48, Julien Grall wrote:
> Hi Oleksandr,
Hi Julien


> On 20/12/2021 21:15, Oleksandr Tyshchenko wrote:
> > 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.
> Looking at the code, it is not possible to share the micro-TLB between 
> domains (or even Xen). So technically, we will still want to {, 
> un}hotplug the devices using the same u-TLB together.
> Therefore, I would clarify that this is necessary because even if we 
> have to remove all the devices together, the IOMMU driver will be 
> de-assigning them one-by-one.
> I would add a similar comment in the code as well.
ok, will add.


> > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> > Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> > ---
> > Changes V1 -> V2:
> >     - add R-b
> >     - add ASSERT() in ipmmu_utlb_disable()
> > ---
> >   xen/drivers/passthrough/arm/ipmmu-vmsa.c | 19 +++++++++++--------
> >   1 file changed, 11 insertions(+), 8 deletions(-)
> >
> > diff --git a/xen/drivers/passthrough/arm/ipmmu-vmsa.c 
> > b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
> > index 649b9f6..1224ea4 100644
> > --- a/xen/drivers/passthrough/arm/ipmmu-vmsa.c
> > +++ b/xen/drivers/passthrough/arm/ipmmu-vmsa.c
> > @@ -127,6 +127,7 @@ 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;
> >   };
> >   @@ -467,13 +468,12 @@ 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;
> >   }
> > @@ -484,7 +484,10 @@ static void ipmmu_utlb_disable(struct 
> > ipmmu_vmsa_domain *domain,
> >   {
> >       struct ipmmu_vmsa_device *mmu = domain->mmu;
> >   -    ipmmu_imuctr_write(mmu, utlb, 0);
> > +    ASSERT(mmu->utlb_refcount[utlb] > 0);
> > +
> > +    if ( --mmu->utlb_refcount[utlb] == 0 )
> > +        ipmmu_imuctr_write(mmu, utlb, 0);
> >   }
> >     /* Domain/Context Management */
> Cheers,
--
Regards,

Oleksandr Tyshchenko