Re: [PATCH v1 1/3] iommu/vt-d: Only clear real DMA device's context entries

[Lu Baolu <baolu.lu@linux.intel.com>]

On 2020/5/28 0:56, Jon Derrick wrote:
> Domain context mapping can encounter issues with sub-devices of a real
> DMA device. A sub-device cannot have a valid context entry due to it
> potentially aliasing another device's 16-bit ID. It's expected that
> sub-devices of the real DMA device uses the real DMA device's requester
> when context mapping.
> 
> This is an issue when a sub-device is removed where the context entry is
> cleared for all aliases. Other sub-devices are still valid, resulting in
> those sub-devices being stranded without valid context entries.
> 
> The correct approach is to use the real DMA device when programming the
> context entries. The insertion path is correct because device_to_iommu()
> will return the bus and devfn of the real DMA device. The removal path
> needs to only operate on the real DMA device, otherwise the entire
> context entry would be cleared for all sub-devices of the real DMA
> device.
> 
> This patch also adds a helper to determine if a struct device is a
> sub-device of a real DMA device.
> 
> Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>

Fixes: 2b0140c69637e ("iommu/vt-d: Use pci_real_dma_dev() for mapping")
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>

Best regards,
baolu