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

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Message-ID: <b54491c4-c119-6e83-93ae-d0df7fc165a1@infradead.org>
Date:   Fri, 16 Nov 2018 08:59:28 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Souptick Joarder <jrdr.linux@...il.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     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 11/16/18 12:15 AM, Souptick Joarder wrote:
> On Fri, Nov 16, 2018 at 12:11 PM Matthew Wilcox <willy@...radead.org> wrote:
>>
>> On Fri, Nov 16, 2018 at 11:00:30AM +0530, Souptick Joarder wrote:
>>> On Thu, Nov 15, 2018 at 11:44 PM Randy Dunlap <rdunlap@...radead.org> wrote:
>>>> On 11/15/18 7:45 AM, Souptick Joarder wrote:
>>>> What is the opposite of vm_insert_range() or even of vm_insert_page()?
>>>> or is there no need for that?
>>>
>>> There is no opposite function of vm_insert_range() / vm_insert_page().
>>> My understanding is, in case of any error, mmap handlers will return the
>>> err to user process and user space will decide the next action. So next
>>> time when mmap handler is getting invoked it will map from the beginning.
>>> Correct me if I am wrong.
>>
>> The opposite function, I suppose, is unmap_region().
>>
>>>> s/no./number/
>>>
>>> I didn't get it ??
>>
>> This is a 'sed' expression.  's' is the 'substitute' command; the /
>> is a separator, 'no.' is what you wrote, and 'number' is what Randy
>> is recommending instead.
> 
> Ok. Will change it in v2.

Thanks.

>>>>> +     for (i = 0; i < page_count; i++) {
>>>>> +             ret = vm_insert_page(vma, uaddr, pages[i]);
>>>>> +             if (ret < 0)
>>>>> +                     return ret;
>>>>
>>>> For a non-trivial value of page_count:
>>>> Is it a problem if vm_insert_page() succeeds for several pages
>>>> and then fails?
>>>
>>> No, it will be considered as total failure and mmap handler will return
>>> the err to user space.
>>
>> I think what Randy means is "What happens to the inserted pages?" and
>> the answer is that mmap_region() jumps to the 'unmap_and_free_vma'
>> label, which is an accurate name.

which says:

	/* Undo any partial mapping done by a device driver. */
	unmap_region(mm, vma, prev, vma->vm_start, vma->vm_end);

and that is what I was missing.  Thanks.

> Sorry for incorrect understanding of the question.

No problem.


-- 
~Randy