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

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Message-ID: <aBzl+mn+N4bnUsPN@nvidia.com>
Date: Thu, 8 May 2025 10:12:26 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Vasant Hegde <vasant.hegde@....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 Thu, May 08, 2025 at 09:14:56AM -0300, Jason Gunthorpe wrote:
> On Wed, May 07, 2025 at 10:56:17PM -0700, Nicolin Chen wrote:
> 
> > What I am not sure is if the HW allows setting the ComWaitIntEn bit
> > after CmdBufEn=1, which seems to be unlikely but the spec does not
> > highlight. If so, this would be an modification to the HW QUEUE, in
> > which case we could either do an relocation of the HW QUEUE (where
> > we can set the flag in the 2nd allocation) or add an new option via
> > IOMMUFD_CMD_OPTION (as Kevin suggested), and I think it should be
> > a per-HW_QUEUE option since it doesn't affect other type of queues
> > like Event/PRR Log Buffers.
> 
> The main question is if the control is global to the entire VIOMMU and
> all its HW QUEUE's or local to a single HW QUEUE.

Oh, that's right.. I recall AMD only has one Command Buffer,
but can have dual Event Log Buffers and dual PPR Log Buffers.

And the EventIntEn or PprIntEn bit seem to be global for the
dual buffers..

> If it is global then some "modify viommu" operation should be used to
> change it.
>
> If it is local then some "modify hw queu" operation.
>
> IOMMUFD_CMD_OPTION could be used with an object_id == VIOMMU as a kind
> of modify..

Vasant can confirm. But looks like it should be a vIOMMU
option.

Thanks
Nicolin