linux-kernel - Re: [PATCH v12 2/8] iommu: Move global PASID allocation from SVA to core

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Date:   Fri, 4 Aug 2023 10:51:46 -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 v12 2/8] iommu: Move global PASID allocation from SVA to
 core

On Wed, Aug 02, 2023 at 02:24:21PM -0700, Jacob Pan wrote:
> 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.
> 
> This patch moves global PASID allocation APIs from SVA to IOMMU APIs.
> Reserved PASIDs, currently only RID_PASID, are excluded from the global
> PASID allocation.
> 
> It is expected that device drivers will use the allocated PASIDs to
> attach to appropriate IOMMU domains for use.
> 
> Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
> v8: fix off-by-one in max_pasid check
> v7: simplify range check (Baolu)
> v6: explicitly exclude reserved a range from SVA PASID allocation
>     check mm PASID compatibility with device
> v5: move PASID range check inside API so that device drivers only pass
>     in struct device* (Kevin)
> v4: move dummy functions outside ifdef CONFIG_IOMMU_SVA (Baolu)
> ---
>  drivers/iommu/iommu-sva.c | 29 ++++++++++-------------------
>  drivers/iommu/iommu.c     | 28 ++++++++++++++++++++++++++++
>  include/linux/iommu.h     | 10 ++++++++++
>  3 files changed, 48 insertions(+), 19 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason