Patch "xen: assume XENFEAT_gnttab_map_avail_bits being set for pv guests" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    xen: assume XENFEAT_gnttab_map_avail_bits being set for pv guests

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     xen-assume-xenfeat_gnttab_map_avail_bits-being-set-f.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d6435ea3208226d59ffeae497311f5ad7759d1d8
Author: Juergen Gross <jgross@xxxxxxxx>
Date:   Fri Jul 30 09:18:04 2021 +0200

    xen: assume XENFEAT_gnttab_map_avail_bits being set for pv guests
    
    [ Upstream commit 30dcc56bba911db561c35d4131baf983a41023f8 ]
    
    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>
    Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20210730071804.4302-4-jgross@xxxxxxxx
    Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
    Stable-dep-of: 5c13a4a0291b ("xen/gntdev: Accommodate VMA splitting")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 54fee4087bf1..5dd9d1ac755e 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -289,20 +289,13 @@ 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);
@@ -311,14 +304,6 @@ 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)
 {
 	size_t alloced = 0;
@@ -1102,23 +1087,6 @@ 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;