linux-kernel - Re: [PATCH v5 5/6] iommu: Support mm PASID 1:n with sva domains

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Date:   Thu, 5 Oct 2023 15:49:57 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Tina Zhang <tina.zhang@...el.com>
Cc:     Kevin Tian <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Michael Shavit <mshavit@...gle.com>,
        Vasant Hegde <vasant.hegde@....com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 5/6] iommu: Support mm PASID 1:n with sva domains

On Mon, Sep 25, 2023 at 10:38:12AM +0800, Tina Zhang wrote:
> Each mm bound to devices gets a PASID and corresponding sva domains
> allocated in iommu_sva_bind_device(), which are referenced by iommu_mm
> field of the mm. The PASID is released in __mmdrop(), while a sva domain
> is released when no one is using it (the reference count is decremented
> in iommu_sva_unbind_device()). However, although sva domains and their
> PASID are separate objects such that their own life cycles could be
> handled independently, an enqcmd use case may require releasing the
> PASID in releasing the mm (i.e., once a PASID is allocated for a mm, it
> will be permanently used by the mm and won't be released until the end
> of mm) and only allows to drop the PASID after the sva domains are
> released. To this end, mmgrab() is called in iommu_sva_domain_alloc() to
> increment the mm reference count and mmdrop() is invoked in
> iommu_domain_free() to decrement the mm reference count.
> 
> Since the required info of PASID and sva domains is kept in struct
> iommu_mm_data of a mm, use mm->iommu_mm field instead of the old pasid
> field in mm struct. The sva domain list is protected by iommu_sva_lock.
> 
> Besides, this patch removes mm_pasid_init(), as with the introduced
> iommu_mm structure, initializing mm pasid in mm_init() is unnecessary.
> 
> Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Vasant Hegde <vasant.hegde@....com>
> Signed-off-by: Tina Zhang <tina.zhang@...el.com>
> ---
> 
> Change in v5:
> - Use smp_store_release() & READ_ONCE() in storing and loading mm's
>   pasid value.
> 
> Change in v4:
> - Rebase to v6.6-rc1.
> 
>  drivers/iommu/iommu-sva.c | 40 +++++++++++++++++++++++++++------------
>  include/linux/iommu.h     | 18 +++++++++++-------
>  kernel/fork.c             |  1 -
>  3 files changed, 39 insertions(+), 20 deletions(-)

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

Jason