s390/pageattr: do a single TLB flush for change_page_attr

The change of the access rights for an address range in the kernel
address space is currently done with a loop of IPTE + a store of the
modified PTE. Between the IPTE and the store the PTE will be invalid,
this intermediate state can cause problems with concurrent accesses.

Consider a change of a kernel area from read-write to read-only, a
concurrent reader of that area should be fine but with the invalid
PTE it might get an unexpected exception.

Remove the IPTEs for each PTE and do a global flush after all PTEs
have been modified.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c
index 749c98407b41..f2a5c29a97e9 100644
--- a/arch/s390/mm/pageattr.c
+++ b/arch/s390/mm/pageattr.c
@@ -65,19 +65,17 @@ static pte_t *walk_page_table(unsigned long addr)
 static void change_page_attr(unsigned long addr, int numpages,
                              pte_t (*set) (pte_t))
 {
-        pte_t *ptep, pte;
+        pte_t *ptep;
         int i;
 
         for (i = 0; i < numpages; i++) {
                 ptep = walk_page_table(addr);
                 if (WARN_ON_ONCE(!ptep))
                         break;
-                pte = *ptep;
-                pte = set(pte);
-                __ptep_ipte(addr, ptep);
-                *ptep = pte;
+                *ptep = set(*ptep);
                 addr += PAGE_SIZE;
         }
+        __tlb_flush_kernel();
 }
 
 int set_memory_ro(unsigned long addr, int numpages)