memblock_reserve or memblock_remove to reserve a page

[Nikhil Utane]

Hi,

This is the hole that we see in system RAM.
Shouldn't the 0xA4D page be out of limit for Linux Kernel?

# cat /proc/iomem
00000000-00a4cfff : System RAM
00a4d000-00a4dfff : csSIGILL
00a4e000-bfffffff : System RAM

-Regards
Nikhil

On Wed, Sep 28, 2016 at 6:55 PM, Nikhil Utane <nikhil.subscribed at gmail.com>
wrote:

> base1 = 0xA4D000; size1=0x1000;
> memblock_reserve (base1, size1);
>
> (In a separate static driver code)
> request_mem_region_exclusive (0x00A4D000, 4096, "csSIGILL")
>
> If a driver requests for a memory region, shouldn't the kernel then not
> allocate it for any other purpose?
>
> -Regards
> Nikhil
>
> On Wed, Sep 28, 2016 at 3:12 PM, Arun Sudhilal <getarunks at gmail.com>
> wrote:
>
>> Hello Nikhil,
>>
>> On Wed, Sep 28, 2016 at 2:41 PM, Nikhil Utane
>> <nikhil.subscribed at gmail.com> wrote:
>> > Arun,
>> >
>> > What seems to have done the trick is calling memblock_remove() followed
>> by a
>> > call to request_mem_region(). This creates a hole which can be
>> confirmed in
>> > the output of /proc/iomem.
>> >
>> > Do you see any issue with this approach?
>>
>> I really don't know how it works for you. Marking address of a page as
>> iomem.  How buddy allocator ignores this page?
>> request_mem_region() is a way of managing IO resource memory, to avoid
>> two drivers using same IO memory. It has not relation with buddy
>> allocator.
>>
>> Can you post code snippet?
>>
>> Regards,
>> Arun
>>
>> >
>> > -Thanks
>> > Nikhil
>> >
>> > On Tue, Sep 27, 2016 at 4:14 PM, Arun Sudhilal <getarunks at gmail.com>
>> wrote:
>> >>
>> >> Hello Nikhil,
>> >>
>> >> On Fri, Sep 9, 2016 at 7:01 AM, Nikhil Utane
>> >> <nikhil.subscribed at gmail.com> wrote:
>> >> > I want to reserve a physical memory page with a fixed PFN. I do not
>> want
>> >> > this page to be used by anyone else. I am calling memblock_reserve()
>> to
>> >> > supposedly reserve the page. I am writing some content into this
>> page.
>> >> > What
>> >> > I see is that during some runs the content of this page is modified
>> >> > (either
>> >> > fully or sometimes partially). In few runs, I see it as intact. Is it
>> >> > expected that even after calling memblock_reserve() the kernel can
>> >> > allocate
>> >> > this physical page for any other purpose? How is memblock_remove()
>> >> > different
>> >> > from memblock_reserve? I tried reading up but didn't see any useful
>> >> > information. What I understood is memblock_remove will completely
>> remove
>> >> > from kernel's allocation mechanism. Should I then be using remove
>> >> > instead of
>> >> > reserve?
>> >>
>> >> when a DT entry is added to  #reserved-memory node, what
>> >> drivers/of/fdt.c does is to call memblock_remove() and
>> >> memblock_reserve().
>> >> This happens after the memblock driver is initialized but before buddy
>> >> allocator up. Did you try this approach? This should work for you.
>> >>
>> >> Only option once the kernel boot is complete is to try out the
>> >> technique what mm/memory_hotplug.c does while offline memory.
>> >> isolate_page_range and then migrate.
>> >>
>> >> Regards,
>> >> Arun
>> >>
>> >>
>> >> >
>> >> > -Thanks
>> >> > Nikhil
>> >> >
>> >> > _______________________________________________
>> >> > Kernelnewbies mailing list
>> >> > Kernelnewbies at kernelnewbies.org
>> >> > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>> >> >
>> >
>> >
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20160929/56a7df6a/attachment.html