kaiser: drop is_atomic arg to kaiser_pagetable_walk()

I have not observed a might_sleep() warning from setup_fixmap_gdt()'s
use of kaiser_add_mapping() in our tree (why not?), but like upstream
we have not provided a way for that to pass is_atomic true down to
kaiser_pagetable_walk(), and at startup it's far from a likely source
of trouble: so just delete the walk's is_atomic arg and might_sleep().
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

CVE-2017-5754
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/mm/kaiser.c

@@ -108,19 +108,13 @@ static inline unsigned long get_pa_from_mapping(unsigned long vaddr)
  *
  * Returns a pointer to a PTE on success, or NULL on failure.
  */
-static pte_t *kaiser_pagetable_walk(unsigned long address, bool is_atomic)
+static pte_t *kaiser_pagetable_walk(unsigned long address)
 {
 	pmd_t *pmd;
 	pud_t *pud;
 	pgd_t *pgd = native_get_shadow_pgd(pgd_offset_k(address));
 	gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO);
 
-	if (is_atomic) {
-		gfp &= ~GFP_KERNEL;
-		gfp |= __GFP_HIGH | __GFP_ATOMIC;
-	} else
-		might_sleep();
-
 	if (pgd_none(*pgd)) {
 		WARN_ONCE(1, "All shadow pgds should have been populated");
 		return NULL;
@@ -195,7 +189,7 @@ static int kaiser_add_user_map(const void *__start_addr, unsigned long size,
 			ret = -EIO;
 			break;
 		}
-		pte = kaiser_pagetable_walk(address, false);
+		pte = kaiser_pagetable_walk(address);
 		if (!pte) {
 			ret = -ENOMEM;
 			break;