[PATCH 3/3] xen: assume XENFEAT_gnttab_map_avail_bits being set for pv guests

[Juergen Gross <jgross@xxxxxxxx>]

XENFEAT_gnttab_map_avail_bits is always set in Xen 4.0 and newer.
Remove coding assuming it might be zero.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/gntdev.c | 36 ++----------------------------------
 1 file changed, 2 insertions(+), 34 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index f01d58c7a042..93818816e137 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -266,20 +266,13 @@ static int find_grant_ptes(pte_t *pte, unsigned long 
addr, void *data)
 {
        struct gntdev_grant_map *map = data;
        unsigned int pgnr = (addr - map->vma->vm_start) >> PAGE_SHIFT;
-       int flags = map->flags | GNTMAP_application_map | GNTMAP_contains_pte;
+       int flags = map->flags | GNTMAP_application_map | GNTMAP_contains_pte |
+                   (1 << _GNTMAP_guest_avail0);
        u64 pte_maddr;
 
        BUG_ON(pgnr >= map->count);
        pte_maddr = arbitrary_virt_to_machine(pte).maddr;
 
-       /*
-        * Set the PTE as special to force get_user_pages_fast() fall
-        * back to the slow path.  If this is not supported as part of
-        * the grant map, it will be done afterwards.
-        */
-       if (xen_feature(XENFEAT_gnttab_map_avail_bits))
-               flags |= (1 << _GNTMAP_guest_avail0);
-
        gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, flags,
                          map->grants[pgnr].ref,
                          map->grants[pgnr].domid);
@@ -288,14 +281,6 @@ static int find_grant_ptes(pte_t *pte, unsigned long addr, 
void *data)
        return 0;
 }
 
-#ifdef CONFIG_X86
-static int set_grant_ptes_as_special(pte_t *pte, unsigned long addr, void 
*data)
-{
-       set_pte_at(current->mm, addr, pte, pte_mkspecial(*pte));
-       return 0;
-}
-#endif
-
 int gntdev_map_grant_pages(struct gntdev_grant_map *map)
 {
        int i, err = 0;
@@ -1053,23 +1038,6 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
                err = vm_map_pages_zero(vma, map->pages, map->count);
                if (err)
                        goto out_put_map;
-       } else {
-#ifdef CONFIG_X86
-               /*
-                * If the PTEs were not made special by the grant map
-                * hypercall, do so here.
-                *
-                * This is racy since the mapping is already visible
-                * to userspace but userspace should be well-behaved
-                * enough to not touch it until the mmap() call
-                * returns.
-                */
-               if (!xen_feature(XENFEAT_gnttab_map_avail_bits)) {
-                       apply_to_page_range(vma->vm_mm, vma->vm_start,
-                                           vma->vm_end - vma->vm_start,
-                                           set_grant_ptes_as_special, NULL);
-               }
-#endif
        }
 
        return 0;
-- 
2.26.2