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SubjectRe: Nick's core remove PageReserved broke vmware...
Petr Vandrovec wrote:
> Hello Nick,
> what's the reason behind disallowing get_user_pages() on VM_RESERVED
> regions? vmmon uses VM_RESERVED on its 'vma' as otherwise some kernels
> used by SUSE complained loudly about mismatch between PageReserved() and
> VM_RESERVED flags.
>

Hi Petr,

The reason is that VM_RESERVED indicates that the core vm is not allowed
to touch any 'struct page' through this mapping, which get_user_pages
would do.

> I'll remove it from vmmon for >= 2.6.14 kernels as that bogus test
> never made to Linux kernel, but I cannot find any reason why
> get_user_pages() should not work on VM_RESERVED (or VM_IO for that
> matter) user pages. Can you show me reasoning behind that decision ?

The reasoning behind the decision was so VM_RESERVED is usable for a
complete replacement to PageReserved. For example mappings through
/dev/mem should not touch the page count.

You may be able to go a step further and clear PageReserved from your
pages as well, and thus have a working driver without special casing
for both kernels.

Thanks,
Nick

--
SUSE Labs, Novell Inc.

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