Re: [PATCH v3 4/5] PCI: vmd: Stop overriding dma_map_ops

[Christoph Hellwig <hch@lst.de>]

On Fri, Jan 10, 2020 at 10:21:12AM -0700, Jon Derrick wrote:
> Devices on the VMD domain use the VMD endpoint's requester ID and have
> been relying on the VMD endpoint's DMA operations. The problem with this
> was that VMD domain devices would use the VMD endpoint's attributes when
> doing DMA and IOMMU mapping. We can be smarter about this by only using
> the VMD endpoint when mapping and providing the correct child device's
> attributes during DMA operations.
> 
> This patch modifies Intel-IOMMU to check for a 'Direct DMA Alias' and
> refer to it for mapping.
> 
> Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
> ---
>  drivers/iommu/intel-iommu.c    |  18 +++--
>  drivers/pci/controller/Kconfig |   1 -
>  drivers/pci/controller/vmd.c   | 150 -----------------------------------------
>  3 files changed, 13 insertions(+), 156 deletions(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 716347e2..7ca807a 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -804,14 +804,14 @@ static struct intel_iommu *device_to_iommu(struct device *dev, u8 *bus, u8 *devf
>  
>  	if (dev_is_pci(dev)) {
>  		struct pci_dev *pf_pdev;
> +		struct pci_dev *dma_alias;
>  
>  		pdev = to_pci_dev(dev);
>  
> -#ifdef CONFIG_X86
> -		/* VMD child devices currently cannot be handled individually */
> -		if (is_vmd(pdev->bus))
> -			return NULL;
> -#endif

Don't we need this sanity check to prevent assingning vmd subdevices?

> +		/* DMA aliased devices use the DMA alias's IOMMU */
> +		dma_alias = pci_direct_dma_alias(pdev);
> +		if (dma_alias)
> +			pdev = dma_alias;
>  
>  		/* VFs aren't listed in scope tables; we need to look up
>  		 * the PF instead to find the IOMMU. */
> @@ -2521,6 +2521,14 @@ struct dmar_domain *find_domain(struct device *dev)
>  		     dev->archdata.iommu == DUMMY_DEVICE_DOMAIN_INFO))
>  		return NULL;
>  
> +	if (dev_is_pci(dev)) {
> +		struct pci_dev *pdev = to_pci_dev(dev);
> +		struct pci_dev *dma_alias = pci_direct_dma_alias(pdev);
> +
> +		if (dma_alias)
> +			dev = &dma_alias->dev;

Instead of all these duplicate calls, shouldn't pci_direct_dma_alias be
replaced with a pci_real_dma_dev helper that either returns the
dma parent if it exiѕts, or the actual device?

Also I think this patch should be split - one for intel-iommu that
just adds the real device checks, and then one that wires up vmd to
the new mechanism and then removes all the cruft.
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