linux-kernel - Re: [PATCH 1/9] mm: Introduce new vm_insert

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Date:   Wed, 21 Nov 2018 04:35:13 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     William Kucharski <william.kucharski@...cle.com>
Cc:     Souptick Joarder <jrdr.linux@...il.com>, rppt@...ux.ibm.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        vbabka@...e.cz, Rik van Riel <riel@...riel.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        rppt@...ux.vnet.ibm.com, Peter Zijlstra <peterz@...radead.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        robin.murphy@....com, iamjoonsoo.kim@....com, treding@...dia.com,
        Kees Cook <keescook@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        stefanr@...6.in-berlin.de, hjc@...k-chips.com,
        Heiko Stuebner <heiko@...ech.de>, airlied@...ux.ie,
        oleksandr_andrushchenko@...m.com, joro@...tes.org,
        pawel@...iak.com, Kyungmin Park <kyungmin.park@...sung.com>,
        mchehab@...nel.org, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux1394-devel@...ts.sourceforge.net,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org, xen-devel@...ts.xen.org,
        iommu@...ts.linux-foundation.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 1/9] mm: Introduce new vm_insert_range API

On Wed, Nov 21, 2018 at 04:19:11AM -0700, William Kucharski wrote:
> Could you add a line to the description explicitly stating that a failure
> to insert any page in the range will fail the entire routine, something
> like:
> 
> > * This allows drivers to insert range of kernel pages they've allocated
> > * into a user vma. This is a generic function which drivers can use
> > * rather than using their own way of mapping range of kernel pages into
> > * user vma.
> > *
> > * A failure to insert any page in the range will fail the call as a whole.
> 
> It's obvious when reading the code, but it would be self-documenting to
> state it outright.

It's probably better to be more explicit and answer Randy's question:

 * If we fail to insert any page into the vma, the function will return
 * immediately leaving any previously-inserted pages present.  Callers
 * from the mmap handler may immediately return the error as their
 * caller will destroy the vma, removing any successfully-inserted pages.
 * Other callers should make their own arrangements for calling unmap_region().

Although unmap_region() is static so there clearly isn't any code in the
kernel today other than in mmap handlers (or fault handlers) that needs to
insert pages into a VMA.