linux-kernel - Re: [PATCH 0/5] Share sva domains with all devices bound to a mm

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Message-ID: <184044ad-880f-5452-727b-f7fd18330c22@linux.intel.com>
Date:   Wed, 9 Aug 2023 08:18:18 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Tina Zhang <tina.zhang@...el.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Kevin Tian <kevin.tian@...el.com>,
        Michael Shavit <mshavit@...gle.com>
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] Share sva domains with all devices bound to a mm

On 2023/8/8 15:49, Tina Zhang wrote:
> A sva domain's lifetime begins with binding a device to a mm and ends
> by releasing all the bound devices from that sva domain. Technically,
> there could be more than one sva domain identified by the mm PASID for
> the use of bound devices issuing DMA transactions.
> 
> To support mm PASID 1:n with sva domains, each mm needs to keep both a
> reference list of allocated sva domains and the corresponding PASID.
> However, currently, mm struct only has one pasid field for sva usage,
> which is used to keep the info of an assigned PASID. That pasid field
> cannot provide sufficient info to build up the 1:n mapping between PASID
> and sva domains.

Is it more appropriate to have the same life cycle for sva domain and mm
pasid? I feel that they represent the same thing, that is, the address
space shared by mm to a device.

Best regards,
baolu

> 
> This patch-set fills the gap by adding an mm_iommu field[1], whose type is
> mm_iommu_data struct, to replace the old pasid field. The introduced
> mm_iommu_data struct keeps info of both a reference list of sva domains
> and an assigned PASID.
> 
> 
> [1]: https://lore.kernel.org/linux-iommu/ZIBxPd1%2FJCAle6yP@nvidia.com/
> 
> 
> The RFC version of this patch-set is here:
> https://lore.kernel.org/linux-iommu/20230707013441.365583-1-tina.zhang@intel.com/
> 
> Tina Zhang (5):
>    iommu: Add mm_get_pasid() helper function
>    iommu: Call helper function to get assigned pasid value
>    mm: Add structure to keep sva information
>    iommu: Support mm PASID 1:n with sva domains
>    mm: Deprecate pasid field
> 
>   arch/x86/kernel/traps.c                       |  2 +-
>   .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c   | 12 ++---
>   drivers/iommu/intel/svm.c                     |  8 +--
>   drivers/iommu/iommu-sva.c                     | 50 ++++++++++++-------
>   include/linux/iommu.h                         | 19 +++++--
>   include/linux/mm_types.h                      |  3 +-
>   kernel/fork.c                                 |  1 -
>   mm/init-mm.c                                  |  3 --
>   8 files changed, 58 insertions(+), 40 deletions(-)
>