Reserve physical page

On Sat, Aug 6, 2011 at 11:35 PM, Thayumanavar S [off-list ref] wrote:

quoted

Hello everyone,
   I am wondering whether it is possible to reserve a particular physical
page in the kernel.
The GFP pages can start from _any_ location, and i cannot find a way to
specify a starting pfn.
I need a few dozen pages to store a bitmap starting at a particular

physical

quoted

page frame number.
   Perhaps i am trying to do this wrong? I am trying to establish a
(one-way) communication between KVM and a guest VM, by assuming that if

KVM

quoted

knows the physical address in the VM , it can access that bitmap.

you can covert pa to pfn to struct page (there are some macros in the
kernel that does this, you grep the kernel source for it) and directly
set the PG_reserved flag of that struct page.

Ok. But in this case i have to ensure that the pfn is not mapped by the
kernel, right?
Will scanning mem_map to find such a pfn help?
I'm wondering if there are regions which are typically 'free' which i can
reserve and use.

Thanks for the reply,
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