linux-kernel - Re: [PATCH v3 11/23] iommufd/viommu: Add IOMMUFD_CMD_VQUEUE

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Message-ID: <20250506120114.GV2260709@nvidia.com>
Date: Tue, 6 May 2025 09:01:14 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Vasant Hegde <vasant.hegde@....com>
Cc: Nicolin Chen <nicolinc@...dia.com>, kevin.tian@...el.com,
	corbet@....net, will@...nel.org, bagasdotme@...il.com,
	robin.murphy@....com, joro@...tes.org, thierry.reding@...il.com,
	vdumpa@...dia.com, jonathanh@...dia.com, shuah@...nel.org,
	jsnitsel@...hat.com, nathan@...nel.org, peterz@...radead.org,
	yi.l.liu@...el.com, mshavit@...gle.com, praan@...gle.com,
	zhangzekun11@...wei.com, iommu@...ts.linux.dev,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kselftest@...r.kernel.org, patches@...ts.linux.dev,
	mochs@...dia.com, alok.a.tiwari@...cle.com,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: Re: [PATCH v3 11/23] iommufd/viommu: Add IOMMUFD_CMD_VQUEUE_ALLOC
 ioctl

On Tue, May 06, 2025 at 02:45:00PM +0530, Vasant Hegde wrote:
> > +/**
> > + * struct iommu_vqueue_alloc - ioctl(IOMMU_VQUEUE_ALLOC)
> > + * @size: sizeof(struct iommu_vqueue_alloc)
> > + * @flags: Must be 0
> > + * @viommu_id: Virtual IOMMU ID to associate the virtual queue with
> > + * @type: One of enum iommu_vqueue_type
> > + * @index: The logical index to the virtual queue per virtual IOMMU, for a multi
> > + *         queue model
> > + * @out_vqueue_id: The ID of the new virtual queue
> > + * @addr: Base address of the queue memory in the guest physical address space
> > + * @length: Length of the queue memory in the guest physical address space
> > + *
> > + * Allocate a virtual queue object for a vIOMMU-specific HW-acceleration feature
> > + * that allows HW to access a guest queue memory described by @addr and @length.
> > + * It's suggested for VMM to back the queue memory using a single huge page with
> > + * a proper alignment for its contiguity in the host physical address space. The
> > + * call will fail, if the queue memory is not contiguous in the physical address
> > + * space. Upon success, its underlying physical pages will be pinned to prevent
> > + * VMM from unmapping them in the IOAS, until the virtual queue gets destroyed.
> > + *
> > + * A vIOMMU can allocate multiple queues, but it must use a different @index to
> > + * separate each allocation, e.g. VCMDQ0, VCMDQ1, ...
> 
> This will handle multiple queues. But AMD vIOMMU needs to comunicate certain
> control bit setting which is not related to buffers like "Completion wait
> interrupt".
> 
> How do we handle that? extend iommu_queue_alloc() or have different interface?

Do you need a modify queue operation?

Jason