• David Vrabel's avatar
    Revert "xen: properly account for _PAGE_NUMA during xen pte translations" · 5926f87f
    David Vrabel authored
    This reverts commit a9c8e4be.
    
    PTEs in Xen PV guests must contain machine addresses if _PAGE_PRESENT
    is set and pseudo-physical addresses is _PAGE_PRESENT is clear.
    
    This is because during a domain save/restore (migration) the page
    table entries are "canonicalised" and uncanonicalised". i.e., MFNs are
    converted to PFNs during domain save so that on a restore the page
    table entries may be rewritten with the new MFNs on the destination.
    This canonicalisation is only done for PTEs that are present.
    
    This change resulted in writing PTEs with MFNs if _PAGE_PROTNONE (or
    _PAGE_NUMA) was set but _PAGE_PRESENT was clear.  These PTEs would be
    migrated as-is which would result in unexpected behaviour in the
    destination domain.  Either a) the MFN would be translated to the
    wrong PFN/page; b) setting the _PAGE_PRESENT bit would clear the PTE
    because the MFN is no longer owned by the domain; or c) the present
    bit would not get set.
    
    Symptoms include "Bad page" reports when munmapping after migrating a
    domain.
    Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
    Acked-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    Cc: <stable@vger.kernel.org>        [3.12+]
    5926f87f
pgtable.h 21 KB