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

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Message-ID: <8dfb4ad6-5e98-4050-9cb1-888c01340ee8@amd.com>
Date: Thu, 24 Apr 2025 16:51:48 +0530
From: Vasant Hegde <vasant.hegde@....com>
To: Nicolin Chen <nicolinc@...dia.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 4/23/2025 1:15 PM, Nicolin Chen wrote:
> 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
>  };

Nice. Thanks for the details.

-Vasant