x86/xen: safely map and unmap grant frames when in atomic context

arch_gnttab_map_frames() and arch_gnttab_unmap_frames() are called in
atomic context but were calling alloc_vm_area() which might sleep.

Also, if a driver attempts to allocate a grant ref from an interrupt
and the table needs expanding, then the CPU may already by in lazy MMU
mode and apply_to_page_range() will BUG when it tries to re-enable
lazy MMU mode.

These two functions are only used in PV guests.

Introduce arch_gnttab_init() to allocates the virtual address space in
advance.

Avoid the use of apply_to_page_range() by using saving and using the
array of PTE addresses from the alloc_vm_area() call.

N.B. 'alloc_vm_area' pre-allocates the pagetable so there is no need
to worry about having to do a PGD/PUD/PMD walk (like apply_to_page_range
does) and we can instead do set_pte.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
----
[v2: Add comment about alloc_vm_area]
[v3: Fix compile error found by 0-day bot]

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 5d4de88fe5b8..eeba7544f0cd 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -1195,18 +1195,20 @@ static int gnttab_expand(unsigned int req_entries)
 int gnttab_init(void)
 {
         int i;
+        unsigned long max_nr_grant_frames;
         unsigned int max_nr_glist_frames, nr_glist_frames;
         unsigned int nr_init_grefs;
         int ret;
 
         gnttab_request_version();
+        max_nr_grant_frames = gnttab_max_grant_frames();
         nr_grant_frames = 1;
 
         /* Determine the maximum number of frames required for the
          * grant reference free list on the current hypervisor.
          */
         BUG_ON(grefs_per_grant_frame == 0);
-        max_nr_glist_frames = (gnttab_max_grant_frames() *
+        max_nr_glist_frames = (max_nr_grant_frames *
                                grefs_per_grant_frame / RPP);
 
         gnttab_list = kmalloc(max_nr_glist_frames * sizeof(grant_ref_t *),
@@ -1223,6 +1225,11 @@ int gnttab_init(void)
                 }
         }
 
+        ret = arch_gnttab_init(max_nr_grant_frames,
+                               nr_status_frames(max_nr_grant_frames));
+        if (ret < 0)
+                goto ini_nomem;
+
         if (gnttab_setup() < 0) {
                 ret = -ENODEV;
                 goto ini_nomem;