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Message-ID: <ZMpsr3FbcEYRs/G8@nvidia.com>
Date: Wed, 2 Aug 2023 11:48:15 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc: LKML <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
Lu Baolu <baolu.lu@...ux.intel.com>,
Joerg Roedel <joro@...tes.org>,
Jean-Philippe Brucker <jean-philippe@...aro.com>,
Robin Murphy <robin.murphy@....com>,
Will Deacon <will@...nel.org>,
"Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>,
"Yu, Fenghua" <fenghua.yu@...el.com>,
Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v11 2/8] iommu: Move global PASID allocation from SVA to
core
On Mon, Jul 24, 2023 at 03:25:32PM -0700, Jacob Pan wrote:
> Global PASID can be used beyond SVA. For example, drivers that use
> Intel ENQCMD to submit work must use global PASIDs in that PASID
> is stored in a per CPU MSR. When such device need to submit work
> for in-kernel DMA with PASID, it must allocate PASIDs from the same
> global number space to avoid conflict.
This is a bit misleading, maybe:
==
Intel ENQCMD requires a single PASID to be shared between multiple
devices, as the PASID is stored in a single MSR register per-process
and userspace can use only that one PASID.
This means that the PASID allocation for any ENQCMD using device driver
must always come from a shared global pool, regardless of what kind of
domain the PASID will be used with.
Split the code for the global PASID allocator into
iommu_alloc/free_global_pasid() so that drivers can attach non-SVA
domains to PASIDs as well.
==
The code looks fine, though I would eventually like to see the SVA
code not hardwired to the global allocator too :\
Jason
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