linux-kernel - Re: [PATCH 4/5] iommu/vt-d: Disallow SVA if devices don't support 64-bit address

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Date:   Tue, 20 Jul 2021 10:27:16 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Sanjay Kumar <sanjay.k.kumar@...el.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] iommu/vt-d: Disallow SVA if devices don't support
 64-bit address

On 2021-07-20 02:38, Lu Baolu wrote:
> When the device and CPU share an address space (such as SVA), the device
> must support the same addressing capability as the CPU. The CPU does not
> consider the addressing ability of any device when managing the page table
> of a process, so the device must have enough addressing ability to bind
> the page table of the process.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>   drivers/iommu/intel/iommu.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index f45c80ce2381..f3cca1dd384d 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -5372,6 +5372,9 @@ static int intel_iommu_enable_sva(struct device *dev)
>   	if (!(iommu->flags & VTD_FLAG_SVM_CAPABLE))
>   		return -ENODEV;
>   
> +	if (!dev->dma_mask || *dev->dma_mask != DMA_BIT_MASK(64))

Careful - VFIO doesn't set DMA masks (since it doesn't use the DMA API), 
so this appears to be relying on another driver having bound previously, 
otherwise the mask would still be the default 32-bit one from 
pci_setup_device(). I'm not sure that's an entirely robust assumption.

Robin.

> +		return -ENODEV;
> +
>   	if (intel_iommu_enable_pasid(iommu, dev))
>   		return -ENODEV;
>   
>