linux-kernel - Re: [PATCH v2 1/2] iommu/virtio: Make use of ops->iotlb_sync

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Message-ID: <20230922124130.GD13795@ziepe.ca>
Date:   Fri, 22 Sep 2023 09:41:30 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        virtualization@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] iommu/virtio: Make use of ops->iotlb_sync_map

On Fri, Sep 22, 2023 at 08:57:19AM +0100, Jean-Philippe Brucker wrote:
> > > They're not strictly equivalent: this check works around a temporary issue
> > > with the IOMMU core, which calls map/unmap before the domain is
> > > finalized.
> > 
> > Where? The above points to iommu_create_device_direct_mappings() but
> > it doesn't because the pgsize_bitmap == 0:
> 
> __iommu_domain_alloc() sets pgsize_bitmap in this case:
> 
>         /*
>          * If not already set, assume all sizes by default; the driver
>          * may override this later
>          */
>         if (!domain->pgsize_bitmap)
>                 domain->pgsize_bitmap = bus->iommu_ops->pgsize_bitmap;

Dirver's shouldn't do that.

The core code was fixed to try again with mapping reserved regions to
support these kinds of drivers.

Jason