Re: [PATCH v3 7/7] iommu/riscv: Paging domain support

[Tomasz Jeznach]

On Wed, May 1, 2024 at 8:52 PM Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx> wrote:
>
> On 5/1/24 4:01 AM, Tomasz Jeznach wrote:
> > +/*
> > + * Send IOTLB.INVAL for whole address space for ranges larger than 2MB.
> > + * This limit will be replaced with range invalidations, if supported by
> > + * the hardware, when RISC-V IOMMU architecture specification update for
> > + * range invalidations update will be available.
> > + */
> > +#define RISCV_IOMMU_IOTLB_INVAL_LIMIT        (2 << 20)
> > +
> > +static void riscv_iommu_iotlb_inval(struct riscv_iommu_domain *domain,
> > +                                 unsigned long start, unsigned long end)
> > +{
> > +     struct riscv_iommu_bond *bond;
> > +     struct riscv_iommu_device *iommu, *prev;
> > +     struct riscv_iommu_command cmd;
> > +     unsigned long len = end - start + 1;
> > +     unsigned long iova;
> > +
> > +     rcu_read_lock();
> > +
> > +     prev = NULL;
> > +     list_for_each_entry_rcu(bond, &domain->bonds, list) {
> > +             iommu = dev_to_iommu(bond->dev);
> > +
> > +             riscv_iommu_cmd_inval_vma(&cmd);
> > +             riscv_iommu_cmd_inval_set_pscid(&cmd, domain->pscid);
> > +             if (len && len >= RISCV_IOMMU_IOTLB_INVAL_LIMIT) {
> > +                     for (iova = start; iova < end; iova += PAGE_SIZE) {
> > +                             riscv_iommu_cmd_inval_set_addr(&cmd, iova);
> > +                             riscv_iommu_cmd_send(iommu, &cmd, 0);
> > +                     }
> > +             } else {
> > +                     riscv_iommu_cmd_send(iommu, &cmd, 0);
> > +             }
> > +
> > +             /*
> > +              * IOTLB invalidation request can be safely omitted if already sent
> > +              * to the IOMMU for the same PSCID, and with domain->bonds list
> > +              * arranged based on the device's IOMMU, it's sufficient to check
> > +              * last device the invalidation was sent to.
> > +              */
> > +             if (iommu == prev)
> > +                     continue;
> > +
> > +             prev = iommu;
> > +             riscv_iommu_cmd_send(iommu, &cmd, 0);
> > +     }
>
> I don't quite follow why not moving "if (iommu == prev)" check to the
> top and removing the last riscv_iommu_cmd_send(). My understanding is
> that we could make it simply like below:
>
>         prev = NULL;
>         list_for_each_entry_rcu(bond, &domain->bonds, list) {
>                 iommu = dev_to_iommu(bond->dev);
>                 if (iommu == prev)
>                         continue;
>
>                 /*
>                  * Send an invalidation request to the request queue
>                  * without wait.
>                  */
>                 ... ...
>
>                 prev = iommu;
>         }
>

Oh. Thanks for spotting that.
Code section reordered very likely during rebasing patches...

> > +
> > +     prev = NULL;
> > +     list_for_each_entry_rcu(bond, &domain->bonds, list) {
> > +             iommu = dev_to_iommu(bond->dev);
> > +             if (iommu == prev)
> > +                     continue;
> > +
> > +             prev = iommu;
> > +             riscv_iommu_cmd_iofence(&cmd);
> > +             riscv_iommu_cmd_send(iommu, &cmd, RISCV_IOMMU_QUEUE_TIMEOUT);
> > +     }
> > +     rcu_read_unlock();
> > +}
>
> Best regards,
> baolu

Best regards,
- Tomasz