Re: [Xen-devel] [PATCH 05/16] xenpaging: update machine_to_phys_mapping during page-in and page-out

[Olaf Hering <olaf@xxxxxxxxx>]

The machine_to_phys_mapping array needs updating during page-out.
If a page is gone, a call to get_gpfn_from_mfn will still return the old
gfn for an already paged-out page.  This happens when the entire guest
ram is paged-out before xen_vga_populate_vram() runs.  Then
XENMEM_populate_physmap is called with gfn 0xff000.  A new page is
allocated with alloc_domheap_pages.  This new page does not have a gfn
yet.  However, in guest_physmap_add_entry() the passed mfn maps still to
an old gfn.  This old gfn is paged-out and has no mfn anymore.  As a
result, the ASSERT() triggers because p2m_is_ram() is true for
p2m_ram_paging* types.

If the machine_to_phys_mapping array is updated properly, both loops in
guest_physmap_add_entry() turn into no-ops for the new page and the
mfn/gfn mapping will be done at the end of the function.


The same thing needs to happen dring a page-in.
If XENMEM_add_to_physmap is used with XENMAPSPACE_gmfn,
get_gpfn_from_mfn() will return an appearently valid gfn.  As a result,
guest_physmap_remove_page() is called.  The ASSERT in p2m_remove_page
triggers because the passed mfn does not match the old mfn for the
passed gfn.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>

---
v2:
  call set_gpfn_from_mfn only if mfn is valid

 xen/arch/x86/mm/p2m.c |    3 +++
 1 file changed, 3 insertions(+)

--- xen-unstable.hg-4.1.22353.orig/xen/arch/x86/mm/p2m.c
+++ xen-unstable.hg-4.1.22353/xen/arch/x86/mm/p2m.c
@@ -2742,6 +2742,7 @@ int p2m_mem_paging_evict(struct p2m_doma
     /* Remove mapping from p2m table */
     p2m_lock(p2m);
     set_p2m_entry(p2m, gfn, _mfn(PAGING_MFN), 0, p2m_ram_paged);
+    set_gpfn_from_mfn(mfn_x(mfn), INVALID_M2P_ENTRY);
     p2m_unlock(p2m);
 
     /* Put the page back so it gets freed */
@@ -2820,6 +2821,8 @@ void p2m_mem_paging_resume(struct p2m_do
     mfn = gfn_to_mfn(p2m, rsp.gfn, &p2mt);
     p2m_lock(p2m);
     set_p2m_entry(p2m, rsp.gfn, mfn, 0, p2m_ram_rw);
+    if ( mfn_valid(mfn) )
+        set_gpfn_from_mfn(mfn_x(mfn), rsp.gfn);
     p2m_unlock(p2m);
 
     /* Unpause domain */

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel