Re: [Xen-devel] [PATCH v2] xen/passthrough: Support a single iommu_domain per xen domain per SMMU

[Robert VanVossen <robert.vanvossen@xxxxxxxxxxxxxxx>]

On 3/24/2015 7:07 AM, Manish Jaggi wrote:
> 
> On Monday 23 March 2015 07:16 PM, Robbie VanVossen wrote:
>> If multiple devices are being passed through to the same domain and they
>> share a single SMMU, then they only require a single iommu_domain.
>>
>> In arm_smmu_assign_dev, before a new iommu_domain is created, the
>> xen_domain->contexts is checked for any iommu_domains that are already
>> assigned to device that uses the same SMMU as the current device. If one
>> is found, attach the device to that iommu_domain. If a new one isn't
>> found, create a new iommu_domain just like before.
>>
>> The arm_smmu_deassign_dev function assumes that there is a single
>> device per iommu_domain. This meant that when the first device was
>> deassigned, the iommu_domain was freed and when another device was
>> deassigned a crash occured in xen.
>>
>> To fix this, a reference counter was added to the iommu_domain struct.
>> When an arm_smmu_xen_device references an iommu_domain, the
>> iommu_domains ref is incremented. When that reference is removed, the
>> iommu_domains ref is decremented. The iommu_domain will only be freed
>> when the ref is 0.
>>
>> Signed-off-by: Robbie VanVossen <robert.vanvossen@xxxxxxxxxxxxxxx>
> Hi,
> Are you adding a PCI passthrough support to Xen ?. I am in process of 
> sending smmu driver patches based on juliens latest code.
>

Nope, I am just working on what this patch describes

Thanks,
Robbie VanVossen
DornerWorks


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