Re: [PATCH RFC 08/12] iommufd: IOCTLs for the io_pagetable

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 28 Mar 2022 16:47:49 -0300
Jason Gunthorpe <jgg@nvidia.com> wrote:

> On Mon, Mar 28, 2022 at 03:57:53PM -0300, Jason Gunthorpe wrote:
> 
> > So, currently AMD and Intel have exactly the same HW feature with a
> > different kAPI..  
> 
> I fixed it like below and made the ordering changes Kevin pointed
> to. Will send next week after the merge window:
> 
> 527e438a974a06 iommu: Delete IOMMU_CAP_CACHE_COHERENCY
> 5cbc8603ffdf20 vfio: Move the Intel no-snoop control off of IOMMU_CACHE
> ebc961f93d1af3 iommu: Introduce the domain op enforce_cache_coherency()
> 79c52a2bb1e60b vfio: Require that devices support DMA cache coherence
> 02168f961b6a75 iommu: Replace uses of IOMMU_CAP_CACHE_COHERENCY with dev_is_dma_coherent()
> 
> '79c can be avoided, we'd just drive IOMMU_CACHE off of
> dev_is_dma_coherent() - but if we do that I'd like to properly
> document the arch/iommu/platform/kvm combination that is using this..

We can try to enforce dev_is_dma_coherent(), as you note it's not going
to affect any x86 users.  arm64 is the only obviously relevant arch that
defines ARCH_HAS_SYNC_DMA_FOR_{DEVICE,CPU} but the device.dma_coherent
setting comes from ACPI/OF firmware, so someone from ARM land will need
to shout if this is an issue.  I think we'd need to back off and go
with documentation if a broken use case shows up.  Thanks,

Alex

 
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index 3c0ac3c34a7f9a..f144eb9fea8e31 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -2269,6 +2269,12 @@ static int amd_iommu_def_domain_type(struct device *dev)
>  	return 0;
>  }
>  
> +static bool amd_iommu_enforce_cache_coherency(struct iommu_domain *domain)
> +{
> +	/* IOMMU_PTE_FC is always set */
> +	return true;
> +}
> +
>  const struct iommu_ops amd_iommu_ops = {
>  	.capable = amd_iommu_capable,
>  	.domain_alloc = amd_iommu_domain_alloc,
> @@ -2291,6 +2297,7 @@ const struct iommu_ops amd_iommu_ops = {
>  		.flush_iotlb_all = amd_iommu_flush_iotlb_all,
>  		.iotlb_sync	= amd_iommu_iotlb_sync,
>  		.free		= amd_iommu_domain_free,
> +		.enforce_cache_coherency = amd_iommu_enforce_cache_coherency,
>  	}
>  };
> 
> Thanks,
> Jason
> 

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