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Date:   Mon, 22 Jul 2019 05:01:30 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     John Hubbard <jhubbard@nvidia.com>, Pavel Machek <pavel@ucw.cz>,
        Christoph Hellwig <hch@infradead.org>, john.hubbard@gmail.com,
        SCheung@nvidia.com, akpm@linux-foundation.org,
        aneesh.kumar@linux.vnet.ibm.com, benh@kernel.crashing.org,
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        paulmck@linux.vnet.ibm.com, ross.zwisler@linux.intel.com,
        sgutti@nvidia.com, torvalds@linux-foundation.org,
        vdavydov.dev@gmail.com
Subject: Re: [PATCH] mm/Kconfig: additional help text for HMM_MIRROR option
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On Mon, Jul 22, 2019 at 08:58:04AM -0300, Jason Gunthorpe wrote:
> No one has given me a satisfactory answer about the restriction
> either.
> 
> The only thing this kconfig controls that could possibly be arch
> specific is the page walking code in hmm_range_snapshot and
> related. 
> 
> Maybe there is/was some arch entanglement there?

The page walking code is supposed to be platform independent.
I did push a branch to the buildbot a few days ago to catch issues,
and the only one found so far is an abuse of pte_index() that can be
trivially fixed.  The other thing I noticed is that the use of some
of the p??_none/protnone/present checks seems inconsistent, but I did
not have time to audit that yet.