Re: [PATCH hmm 0/8] Various error case bug fixes for hmm_range_fault()

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Jerome Glisse <jglisse@redhat.com>,
	Ralph Campbell <rcampbell@nvidia.com>,
	Felix.Kuehling@amd.com
Cc: Philip Yang <Philip.Yang@amd.com>,
	John Hubbard <jhubbard@nvidia.com>,
	amd-gfx@lists.freedesktop.org, linux-mm@kvack.org,
	dri-devel@lists.freedesktop.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH  hmm 0/8] Various error case bug fixes for hmm_range_fault()
Date: Mon, 16 Mar 2020 15:25:40 -0300	[thread overview]
Message-ID: <20200316182540.GA21434@ziepe.ca> (raw)
In-Reply-To: <20200311183506.3997-1-jgg@ziepe.ca>

On Wed, Mar 11, 2020 at 03:34:58PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> The hmm_range_fault() flow is fairly complicated. The scheme allows the
> caller to specify if it needs a usable result for each page, or if it only
> needs the current page table status filled in. This mixture of behavior is
> useful for a caller that wants to build a 'prefetch around fault'
> algorithm.
> 
> Although we have no in-tree users of this capability, I am working on
> having RDMA ODP work in this manner, and removing these bugs from
> hmm_range_fault() is a necessary step.
> 
> The basic principles are:
> 
>  - If the caller did not ask for a VA to be valid then hmm_range_fault()
>    should not fail because of that VA
> 
>  - If 0 is returned from hmm_range_fault() then the entire pfns array
>    contains valid data
> 
>  - HMM_PFN_ERROR is set if faulting fails, or if asking for faulting
>    would fail
> 
>  - A 0 return from hmm_range_fault() does not have HMM_PFN_ERROR in any
>    VA's the caller asked to be valid
> 
> This series does not get there completely, I have a followup series
> closing some more complex cases.
> 
> I tested this series using Ralph's hmm tester he posted a while back,
> other testing would be appreciated.
> 
> Jason Gunthorpe (8):
>   mm/hmm: add missing unmaps of the ptep during hmm_vma_handle_pte()
>   mm/hmm: do not call hmm_vma_walk_hole() while holding a spinlock
>   mm/hmm: add missing pfns set to hmm_vma_walk_pmd()
>   mm/hmm: add missing call to hmm_range_need_fault() before returning
>     EFAULT
>   mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()
>   mm/hmm: return -EFAULT when setting HMM_PFN_ERROR on requested valid
>     pages
>   mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL
>     handling
>   mm/hmm: do not check pmd_protnone twice in hmm_vma_handle_pmd()

I moved these toward linux-next, if others have remarks or tags please
feel free to continue.

>   mm/hmm: don't free the cached pgmap while scanning

I will respin

Thank you all for the reviews!

Regards,
Jason
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