[Xen-devel] Re: Doubt regarding virtual memory mapping from hypervisor to a domain

[Kaustubh Kabra <kaustubhwise@xxxxxxxxx>]

On Mon, Jan 31, 2011 at 9:06 PM, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> wrote:

> From: Kaustubh Kabra [mailto:kaustubhwise@xxxxxxxxx]
> I have allocated few order=9 pages in Xen memory space using
> alloc_domheap_pages(NULL,9,0) during boot time just before domain is
> created (dom0 = domain_create(0, DOMCRF_s3_integrity, DOM0_SSIDREF) in
> xen/arch/x86/setup.c).
>
> I got the following virtual addresses in xen log message-
> (XEN) a2k2: Virt_addr:ffff83011cc00000   MFN:11cc00
> (XEN) a2k2: Virt_addr:ffff83011ca00000   MFN:11ca00
> (XEN) a2k2: Virt_addr:ffff83011c800000   MFN:11c800
> (XEN) a2k2: Virt_addr:ffff83011c600000   MFN:11c600
> (XEN) a2k2: Virt_addr:ffff83011c400000   MFN:11c400
> (XEN) a2k2: Virt_addr:ffff83011c200000   MFN:11c200
> (XEN) a2k2: Virt_addr:ffff83011c000000   MFN:11c000
> (XEN) a2k2: Virt_addr:ffff83011be00000   MFN:11be00
>
> As per config.h file Xen memory map,the virtual mapping shows that the
> memory is  allocated in
> 1:1 direct mapping of all physical memory .Can anyone elaborate
> regarding this mapping ?

It's not clear what you are asking.  Can you be more precise?

> Now can I allocate this mapped memory reserved by Xen hypervisor to
> any domain through any existing or my new hypercall?

Precisely, i want to allocate this mfn to a requesting domain by making a PMD entry. I tried using xen_set_pte and other hugetlb functions but it cannot write as it is in read-only area . So, I passed this new formed PTE formed using this mfn to hypervisor and tried setting the required PMD entry to this new PTE, but xen crashes . 
 

Again, it's not clear what you are asking.  If you are
asking if the guest can map the order=9 page into its
memory space, I think the answer is no.  If you are
asking if Xen can use the memory on behalf of a
domain, for example to copy data from the domain into
Xen (like tmem does), I think the answer is yes.

Also attached are two patches for xen-4.0.1 and jeremy-2.6.32.27 to check the modifications done till now.

-- 
Kaustubh Kabra

xen-patch.patch
Description: Text Data

jeremy2-6-32-27.patch
Description: Text Data

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