Re: [PATCH v3 1/9] mm: Introduce new vm_insert_range API

From: Robin Murphy <robin.murphy@arm.com>
To: Souptick Joarder <jrdr.linux@gmail.com>,
	Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>, Heiko Stuebner <heiko@sntech.de>,
	Peter Zijlstra <peterz@infradead.org>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
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	Kyungmin Park <kyungmin.park@samsung.com>,
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	Andrew Morton <akpm@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v3 1/9] mm: Introduce new vm_insert_range API
Date: Fri, 7 Dec 2018 21:10:00 +0000	[thread overview]
Message-ID: <67495f8f-2092-e42d-321e-5216c346513f@arm.com> (raw)
In-Reply-To: <CAFqt6zYCWOK-uS85GqCzcgT=+YKn1nBrRPq+M9y6eJjmXEKH+g@mail.gmail.com>

On 2018-12-07 7:28 pm, Souptick Joarder wrote:
> On Fri, Dec 7, 2018 at 10:41 PM Matthew Wilcox <willy@infradead.org> wrote:
>>
>> On Fri, Dec 07, 2018 at 03:34:56PM +0000, Robin Murphy wrote:
>>>> +int vm_insert_range(struct vm_area_struct *vma, unsigned long addr,
>>>> +                   struct page **pages, unsigned long page_count)
>>>> +{
>>>> +   unsigned long uaddr = addr;
>>>> +   int ret = 0, i;
>>>
>>> Some of the sites being replaced were effectively ensuring that vma and
>>> pages were mutually compatible as an initial condition - would it be worth
>>> adding something here for robustness, e.g.:
>>>
>>> +     if (page_count != vma_pages(vma))
>>> +             return -ENXIO;
>>
>> I think we want to allow this to be used to populate part of a VMA.
>> So perhaps:
>>
>>          if (page_count > vma_pages(vma))
>>                  return -ENXIO;
> 
> Ok, This can be added.
> 
> I think Patch [2/9] is the only leftover place where this
> check could be removed.

Right, 9/9 could also have relied on my stricter check here, but since 
it's really testing whether it actually managed to allocate vma_pages() 
worth of pages earlier, Matthew's more lenient version won't help for 
that one. (Why privcmd_buf_mmap() doesn't clean up and return an error 
as soon as that allocation loop fails, without taking the mutex under 
which it still does a bunch more pointless work to only undo it again, 
is a mind-boggling mystery, but that's not our problem here...)

Robin.

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