Xen devel - Dec 2009 - [PATCH] x86/mm: early put_page when XENMEM_add_to_physmap(XENMAPSPACE_gmfn)

When using a stub domain, xen massively complains as follows:

(XEN) sh error: sh_remove_all_mappings(): can''t find all mappings of
mfn be3c5: c=8000000000000004 t=00000000
(XEN) sh error: sh_remove_all_mappings(): can''t find all mappings of
mfn be3c4: c=8000000000000004 t=00000000
...

This comes from the XENMEM_add_to_physmap hypercall from hvmloader.

The guest_physmap_remove_page function calls sh_remove_all_mappings()
which checks reference count of the page. Then, calling
guest_physmap_remove_page after temporarily get_page is obviously
wrong. And early put_page is harmless here since domain_lock is
acquired.

Also, the restore program seems not to complain extra mappings
long before. Instead, the stub domain does. Thus the comment in
sh_remove_all_mappings() is rewritten.


Signed-off-by: Kouya Shimura <kouya@jp.fujitsu.com>



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> diff -r 07f98beddc18 xen/arch/x86/mm/shadow/common.c
> --- a/xen/arch/x86/mm/shadow/common.c	Wed Dec 23 08:22:13 2009 +0000
> +++ b/xen/arch/x86/mm/shadow/common.c	Thu Dec 24 14:07:04 2009 +0900
> @@ -2606,7 +2606,7 @@ int sh_remove_all_mappings(struct vcpu *
>      {
>          /* Don''t complain if we''re in HVM and there are
some extra mappings:
>           * The qemu helper process has an untyped mapping of this
dom''s RAM
> -         * and the HVM restore program takes another. */
> +         * and the stub domain takes another. */
>          if ( !(shadow_mode_external(v->domain)
>                 && (page->count_info & PGC_count_mask) <=
3
>                 && (page->u.inuse.type_info &
PGT_count_mask) == 0) )
This change is wrong - the stub domain _is_ the qemu helper process.
(The rest of the patch looks OK).

Tim.

-- 
Tim Deegan <Tim.Deegan@citrix.com>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]

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