On Tue, Jan 28, 2020 at 03:16:06PM -0700, Jordan Crouse wrote:
> Support auxiliary domains for arm-smmu-v2 to initialize and support
> multiple pagetables for a single SMMU context bank. Since the smmu-v2
> hardware doesn't have any built in support for switching the pagetable
> base it is left as an exercise to the caller to actually use the pagetable.
>
> Aux domains are supported if split pagetable (TTBR1) support has been
> enabled on the master domain. Each auxiliary domain will reuse the
> configuration of the master domain. By default the a domain with TTBR1
> support will have the TTBR0 region disabled so the first attached aux
> domain will enable the TTBR0 region in the hardware and conversely the
> last domain to be detached will disable TTBR0 translations. All subsequent
> auxiliary domains create a pagetable but not touch the hardware.
>
> The leaf driver will be able to query the physical address of the
> pagetable with the DOMAIN_ATTR_PTBASE attribute so that it can use the
> address with whatever means it has to switch the pagetable base.
>
> Following is a pseudo code example of how a domain can be created
>
> /* Check to see if aux domains are supported */
> if (iommu_dev_has_feature(dev, IOMMU_DEV_FEAT_AUX)) {
> iommu = iommu_domain_alloc(...);
>
> if (iommu_aux_attach_device(domain, dev))
> return FAIL;
>
> /* Save the base address of the pagetable for use by the driver
> iommu_domain_get_attr(domain, DOMAIN_ATTR_PTBASE, &ptbase);
> }
I'm not really understanding what the pagetable base gets used for here and,
to be honest with you, the whole thing feels like a huge layering violation
with the way things are structured today. Why doesn't the caller just
interface with io-pgtable directly?
Finally, if we need to support context-switching TTBR0 for a live domain
then that code really needs to live inside the SMMU driver because the
ASID and TLB management necessary to do that safely doesn't belong anywhere
else.
Will
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