Re: [Xen-devel] __vmap multiple times same mfn

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 01.03.17 at 06:39, <andr2000@xxxxxxxxx> wrote:
> On 02/28/2017 10:51 PM, Andrew Cooper wrote:
>> On 28/02/17 19:50, Oleksandr Andrushchenko wrote:
>>> I have a use-case when I may need to call __vmap for kernel provided
>>> IPAs (read MFNs)
>>>
>>> which may not be PAGE_SIZE aligned etc.
>>>
>>> The question is if it is safe to call __vmap multiple times for
>>> different IPAs
>>>
>>> sharing the same page (mfn), e.g. map something like 6ca00 0080 and
>>> 6ca00 00a0?
>> What are you trying to do?
> Well, the use-case is as follows: say, there are 2 structures I want to 
> access
> (S1 and S2), S1 occupying pages A'-B-C' and S2 in pages C'-D'
> (I mark with apostrophe here partially occupied pages, e.g. page A is
> partially occupied and B is fully used by S1)
> No guarantee how pages A:D are located in memory
> So, for that reason I want to __vmap A-B-C to access S1 and C-D to access S2

I see no reason why two respective vmap() calls would collide
(provided the cacheability attributes of both mappings don't
conflict). Is there any particular reason why you suspect there
to be a restriction?

Jan


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