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



On 03/01/2017 10:22 AM, Jan Beulich wrote:
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).
For all the mappings I use "PAGE_HYPERVISOR_NOCACHE, VMAP_DEFAULT",
so no problem here
Is there any particular reason why you suspect there
to be a restriction?
No, I have it working on ARM64, just want to be sure it is also
applicable for ARM32/x86
Jan

Thank you

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