Re: [PATCH 1/9] mm: Introduce new vm_insert_range API

From: Randy Dunlap <rdunlap@infradead.org>
To: Souptick Joarder <jrdr.linux@gmail.com>,
	Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@suse.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	vbabka@suse.cz, Rik van Riel <riel@surriel.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	rppt@linux.vnet.ibm.com, Peter Zijlstra <peterz@infradead.org>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	robin.murphy@arm.com, iamjoonsoo.kim@lge.com, treding@nvidia.com,
	Kees Cook <keescook@chromium.org>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	stefanr@s5r6.in-berlin.de, hjc@rock-chips.com,
	Heiko Stuebner <heiko@sntech.de>,
	airlied@linux.ie, oleksandr_andrushchenko@epam.com,
	joro@8bytes.org, pawel@osciak.com,
	Kyungmin Park <kyungmin.park@samsung.com>,
	mchehab@kernel.org, Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Juergen Gross <jgross@suse.com>,
	linux-kernel@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
	linux-arm-kernel@lists.infradead.org,
	linux1394-devel@lists.sourceforge.net,
	dri-devel@lists.freedesktop.org,
	linux-rockchip@lists.infradead.org, xen-devel@lists.xen.org,
	iommu@lists.linux-foundation.org, linux-media@vger.kernel.org
Subject: Re: [PATCH 1/9] mm: Introduce new vm_insert_range API
Date: Fri, 16 Nov 2018 08:59:28 -0800	[thread overview]
Message-ID: <b54491c4-c119-6e83-93ae-d0df7fc165a1@infradead.org> (raw)
In-Reply-To: <CAFqt6zbL1tu4VWtZ5Wz-BgbOS+M2GJziMj958_h_ri4Th3n9bQ@mail.gmail.com>

On 11/16/18 12:15 AM, Souptick Joarder wrote:
> On Fri, Nov 16, 2018 at 12:11 PM Matthew Wilcox <willy@infradead.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@infradead.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