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

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Message-ID: <aAiaiomYczA22xik@Asurada-Nvidia>
Date: Wed, 23 Apr 2025 00:45:14 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Vasant Hegde <vasant.hegde@....com>
CC: <jgg@...dia.com>, <kevin.tian@...el.com>, <corbet@....net>,
	<will@...nel.org>, <robin.murphy@....com>, <joro@...tes.org>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<shuah@...nel.org>, <praan@...gle.com>, <nathan@...nel.org>,
	<peterz@...radead.org>, <yi.l.liu@...el.com>, <jsnitsel@...hat.com>,
	<mshavit@...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>
Subject: Re: [PATCH v1 00/16] iommufd: Add vIOMMU infrastructure (Part-4
 vCMDQ)

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