Re: [PATCH v2 04/19] iommufd: Allow pt_id to carry viommu_id for IOMMU_HWPT_ALLOC

On Thu, Sep 26, 2024 at 04:50:46PM +0800, Yi Liu wrote:

On 2024/8/28 00:59, Nicolin Chen wrote:

quoted

Now a VIOMMU can wrap a shareable nested parent HWPT. So, it can act like
a nested parent HWPT to allocate a nested HWPT.

Support that in the IOMMU_HWPT_ALLOC ioctl handler, and update its kdoc.

Also, associate a viommu to an allocating nested HWPT.

it still not quite clear to me what vIOMMU obj stands for. Here, it is a
wrapper of s2 hpwt IIUC. But in the cover letter, vIOMMU obj can instanced
per the vIOMMU units in VM.

Yea, the implementation in this version is merely a wrapper. I
had a general introduction of vIOMMU in the other reply. And I
will put something similar in the next version of the series,
so the idea would be bigger than a wrapper.

Does it mean each vIOMMU of VM can only have
one s2 HWPT?

Giving some examples here:
 - If a VM has 1 vIOMMU, there will be 1 vIOMMU object in the
   kernel holding one S2 HWPT.
 - If a VM has 2 vIOMMUs, there will be 2 vIOMMU objects in the
   kernel that can hold two different S2 HWPTs, or share one S2
   HWPT (saving memory).

Thanks
Nic