linux-kernel - Re: [PATCH v3 0/5] mm/hmm/nouveau: add PMD system memory mapping

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Date:   Fri, 10 Jul 2020 16:27:04 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Ralph Campbell <rcampbell@...dia.com>
CC:     <linux-rdma@...r.kernel.org>, <linux-mm@...ck.org>,
        <nouveau@...ts.freedesktop.org>, <linux-kselftest@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Jerome Glisse <jglisse@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, Ben Skeggs <bskeggs@...hat.com>
Subject: Re: [PATCH v3 0/5] mm/hmm/nouveau: add PMD system memory mapping

On Wed, Jul 01, 2020 at 03:53:47PM -0700, Ralph Campbell wrote:
> The goal for this series is to introduce the hmm_pfn_to_map_order()
> function. This allows a device driver to know that a given 4K PFN is
> actually mapped by the CPU using a larger sized CPU page table entry and
> therefore the device driver can safely map system memory using larger
> device MMU PTEs.
> The series is based on 5.8.0-rc3 and is intended for Jason Gunthorpe's
> hmm tree. These were originally part of a larger series:
> https://lore.kernel.org/linux-mm/20200619215649.32297-1-rcampbell@nvidia.com/
> 
> Changes in v3:
> Replaced the HMM_PFN_P[MU]D flags with hmm_pfn_to_map_order() to
> indicate the size of the CPU mapping.
> 
> Changes in v2:
> Make the hmm_range_fault() API changes into a separate series and add
>   two output flags for PMD/PUD instead of a single compund page flag as
>   suggested by Jason Gunthorpe.
> Make the nouveau page table changes a separate patch as suggested by
>   Ben Skeggs.
> Only add support for 2MB nouveau mappings initially since changing the
> 1:1 CPU/GPU page table size assumptions requires a bigger set of changes.
> Rebase to 5.8.0-rc3.
> 
> Ralph Campbell (5):
>   nouveau/hmm: fault one page at a time
>   mm/hmm: add hmm_mapping order
>   nouveau: fix mapping 2MB sysmem pages
>   nouveau/hmm: support mapping large sysmem pages
>   hmm: add tests for HMM_PFN_PMD flag

Applied to hmm.git. 

I edited the comment for hmm_pfn_to_map_order() and added a function
to compute the field.

Thanks,
Jason