Re: [PATCH v2 13/40] vfio: Add support for Shared Virtual Addressing

Xu Zaibo
2018-05-29T12:24:28Z

Hi,

On 2018/5/29 19:55, Jean-Philippe Brucker wrote:
> (If possible, please reply in plain text to the list. Reading this in a
> text-only reader is confusing, because all quotes have the same level)
Sorry for that， I have reset the thunderbird, :) thanks.
> On 26/05/18 04:53, Xu Zaibo wrote:
>> I guess there may be some misunderstandings :).
>>
>> From the current patches, 'iommu_sva_device_shutdown' is called by 'vfio_iommu_sva_shutdown', which
>> is mainly used by 'vfio_iommu_type1_detach_group' that is finally called by processes' release of vfio facilitiy
>> automatically or called by 'VFIO_GROUP_UNSET_CONTAINER' manually in the processes.
>>
>> So, just image that 2 processes is working on the device with IOPF feature, and the 2 do the following to enable SVA:
>>
>> 1.open("/dev/vfio/vfio") ;
>>
>> 2.open the group of the devcie by calling open("/dev/vfio/x"), but now,
>> I think the second processes will fail to open the group because current VFIO thinks that one group only can be used by one process/vm,
>> at present, I use mediated device to create more groups on the parent device to support multiple processes;
>>
>> 3.VFIO_GROUP_SET_CONTAINER;
>>
>> 4.VFIO_SET_IOMMU;
>>
>> 5.VFIO_IOMMU_BIND;
> I have a concern regarding your driver. With mdev you can't allow
> processes to program the PASID themselves, since the parent device has a
> single PASID table. You lose all isolation since processes could write
> any value in the PASID field and access address spaces of other
> processes bound to this parent device (even if the BIND call was for
> other mdevs).
Yes, if wrapdrive do nothing on this PASID setting procedure in kernel
space, I think
there definitely exists this security risk.
> The wrap driver has to mediate calls to bind(), and either program the
> PASID into the device itself, or at least check that, when receiving a
> SET_PASID ioctl from a process, the given PASID was actually allocated
> to the process.
Yes, good advice, thanks.
>
>> 6.Do some works with the hardware working unit filled by PASID on the device;
>>
>> 7.VFIO_IOMMU_UNBIND;
>>
>> 8.VFIO_GROUP_UNSET_CONTAINER;---here, have to sleep to wait another process to finish works of the step 6;
>>
>> 9. close(group); close(containner);
>>
>>
>> So, my idea is: If it is possible to just release the params or facilities that only belong to the current process while the process shutdown the device,
>> and while the last process releases them all. Then, as in the above step 8, we
>> don't need to wait, or maybe wait for a very long time if the other process is doing lots of work on the device.
> Given that you need to notify the mediating driver of IOMMU_BIND calls
> as explained above, you could do something similar for shutdown: from
> the mdev driver, call iommu_sva_shutdown_device() only for the last mdev.
Currently, I add an API to check if it is the last mdev in wrapdrive, as
vfio shutdowns the device,
it call the API to do the check at first.

Thanks
Zaibo

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