linux-kernel - Re: [PATCH] mm/Kconfig: additional help text for HMM

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Message-ID: <20190722120130.GA17178@infradead.org>
Date:   Mon, 22 Jul 2019 05:01:30 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     John Hubbard <jhubbard@...dia.com>, Pavel Machek <pavel@....cz>,
        Christoph Hellwig <hch@...radead.org>, john.hubbard@...il.com,
        SCheung@...dia.com, akpm@...ux-foundation.org,
        aneesh.kumar@...ux.vnet.ibm.com, benh@...nel.crashing.org,
        bsingharora@...il.com, dan.j.williams@...el.com,
        dnellans@...dia.com, ebaskakov@...dia.com, hannes@...xchg.org,
        jglisse@...hat.com, kirill.shutemov@...ux.intel.com,
        linux-kernel@...r.kernel.org, liubo95@...wei.com,
        mhairgrove@...dia.com, mhocko@...nel.org,
        paulmck@...ux.vnet.ibm.com, ross.zwisler@...ux.intel.com,
        sgutti@...dia.com, torvalds@...ux-foundation.org,
        vdavydov.dev@...il.com
Subject: Re: [PATCH] mm/Kconfig: additional help text for HMM_MIRROR option

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.