Re: [PATCH v1 00/16] iommufd: Add vIOMMU infrastructure (Part-4 vCMDQ)

[Nicolin Chen <nicolinc@nvidia.com>]

On Wed, Apr 23, 2025 at 12:58:19PM +0530, Vasant Hegde wrote:
> On 4/11/2025 12:07 PM, Nicolin Chen wrote:
> > The vIOMMU object is designed to represent a slice of an IOMMU HW for its
> > virtualization features shared with or passed to user space (a VM mostly)
> > in a way of HW acceleration. This extended the HWPT-based design for more
> > advanced virtualization feature.
> > 
> > A vCMDQ introduced by this series as a part of the vIOMMU infrastructure
> > represents a HW supported queue/buffer for VM to use exclusively, e.g.
> >   - NVIDIA's virtual command queue
> >   - AMD vIOMMU's command buffer
> 
> I assume we can pass multiple buffer details (like GPA, size) from guest to
> hypervisor. Is that correct understanding?

Yes. The NVIDIA model passes through a Virtual-Interface to a VM,
and the VM can allocate and map multiple command queues (buffers)
to the V-Interface, by providing each command queue info in:

+struct iommu_vcmdq_tegra241_cmdqv {
+	__u32 vcmdq_id;
+	__u32 vcmdq_log2size;		// size
+	__aligned_u64 vcmdq_base;	// GPA
 };

Thanks
Nicolin