• Daniel De Graaf's avatar
    xen/gntdev,gntalloc: Remove unneeded VM flags · d79647ae
    Daniel De Graaf authored
    The only time when granted pages need to be treated specially is when
    using Xen's PTE modification for grant mappings owned by another domain
    (that is, only gntdev on PV guests).  Otherwise, the area does not
    require VM_DONTCOPY and VM_PFNMAP, since it can be accessed just like
    any other page of RAM.
    
    Since the vm_operations_struct close operations decrement reference
    counts, a corresponding open function that increments them is required
    now that it is possible to have multiple references to a single area.
    
    We are careful in the gntdev to check if we can remove those flags. The
    reason that we need to be careful in gntdev on PV guests is because we are
    not changing the PFN/MFN mapping on PV; instead, we change the application's
    page tables to point to the other domain's memory. This means that the vma
    cannot be copied without using another grant mapping hypercall; it also
    requires special handling on unmap, which is the reason for gntdev's
    dependency on the MMU notifier.
    
    For gntalloc, this is not a concern - the pages are owned by the domain
    using the gntalloc device, and can be mapped and unmapped in the same manner
    as any other page of memory.
    Acked-by: default avatarIan Campbell <ian.campbell@citrix.com>
    Signed-off-by: default avatarDaniel De Graaf <dgdegra@tycho.nsa.gov>
    Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
    [v2: Added in git commit "We are.." from email correspondence]
    d79647ae
gntdev.c 18.5 KB