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

[Oleksandr Andrushchenko <andr2000@xxxxxxxxx>]

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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