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

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Date: Wed, 1 May 2024 21:39:28 -0700
From: Tomasz Jeznach <tjeznach@...osinc.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
	Anup Patel <apatel@...tanamicro.com>, Sunil V L <sunilvl@...tanamicro.com>, 
	Nick Kossifidis <mick@....forth.gr>, Sebastien Boeuf <seb@...osinc.com>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org, 
	iommu@...ts.linux.dev, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux@...osinc.com
Subject: Re: [PATCH v3 7/7] iommu/riscv: Paging domain support

On Wed, May 1, 2024 at 8:52 PM Baolu Lu <baolu.lu@...ux.intel.com> 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