linux-kernel - Re: [PATCH v2 00/19] iommufd: Add VIOMMU infrastructure (Part-1)

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Message-ID: <ZvxCCp6OuuCMyw8M@Asurada-Nvidia>
Date: Tue, 1 Oct 2024 11:40:10 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Yi Liu <yi.l.liu@...el.com>, Jason Gunthorpe <jgg@...dia.com>
CC: <kevin.tian@...el.com>, <will@...nel.org>, <joro@...tes.org>,
	<suravee.suthikulpanit@....com>, <robin.murphy@....com>,
	<dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>, <shuah@...nel.org>,
	<linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kselftest@...r.kernel.org>,
	<eric.auger@...hat.com>, <jean-philippe@...aro.org>, <mdf@...nel.org>,
	<mshavit@...gle.com>, <shameerali.kolothum.thodi@...wei.com>,
	<smostafa@...gle.com>
Subject: Re: [PATCH v2 00/19] iommufd: Add VIOMMU infrastructure (Part-1)

On Tue, Oct 01, 2024 at 10:48:15AM -0300, Jason Gunthorpe wrote:
> On Sun, Sep 29, 2024 at 03:19:42PM +0800, Yi Liu wrote:
> > > So their viommu HW concepts come along with a requirement that there
> > > be a fixed translation for the VM, which we model by attaching a S2
> > > HWPT to the VIOMMU object which get's linked into the IOMMU HW as
> > > the translation for the queue memory.
> > 
> > Is the mapping of the S2 be static? or it an be unmapped per userspace?
> 
> In principle it should be dynamic, but I think the vCMDQ stuff will
> struggle to do that

Yea. vCMDQ HW requires a setting of the physical address of the
base address to a queue in the VM's ram space. If the S2 mapping
changes (resulting a different queue location in the physical
memory), VMM should notify the kernel for a HW reconfiguration.

I wonder what all the user cases are, which can cause a shifting
of S2 mappings? VM migration? Any others?

Thanks
Nicolin