x86/mm/cpa: Prevent large page split when ftrace flips RW on kernel text

[sfrench/cifs-2.6.git] / arch / x86 / mm / pageattr.c

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 6a9a77a403c928e642a754f68c168ebfa6f7b3c1..e14e95ea7338a3adaf013acb7cd848d909f4dd95 100644 (file)
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -516,7 +516,7 @@ static inline void check_conflict(int warnlvl, pgprot_t prot, pgprotval_t val,
  */
 static inline pgprot_t static_protections(pgprot_t prot, unsigned long start,
                                          unsigned long pfn, unsigned long npg,
-                                         int warnlvl)
+                                         unsigned long lpsize, int warnlvl)
 {
        pgprotval_t forbidden, res;
        unsigned long end;
@@ -535,9 +535,17 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long start,
        check_conflict(warnlvl, prot, res, start, end, pfn, "Text NX");
        forbidden = res;
 
-       res = protect_kernel_text_ro(start, end);
-       check_conflict(warnlvl, prot, res, start, end, pfn, "Text RO");
-       forbidden |= res;
+       /*
+        * Special case to preserve a large page. If the change spawns the
+        * full large page mapping then there is no point to split it
+        * up. Happens with ftrace and is going to be removed once ftrace
+        * switched to text_poke().
+        */
+       if (lpsize != (npg * PAGE_SIZE) || (start & (lpsize - 1))) {
+               res = protect_kernel_text_ro(start, end);
+               check_conflict(warnlvl, prot, res, start, end, pfn, "Text RO");
+               forbidden |= res;
+       }
 
        /* Check the PFN directly */
        res = protect_pci_bios(pfn, pfn + npg - 1);
@@ -819,7 +827,7 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
         * extra conditional required here.
         */
        chk_prot = static_protections(old_prot, lpaddr, old_pfn, numpages,
-                                     CPA_CONFLICT);
+                                     psize, CPA_CONFLICT);
 
        if (WARN_ON_ONCE(pgprot_val(chk_prot) != pgprot_val(old_prot))) {
                /*
@@ -855,7 +863,7 @@ static int __should_split_large_page(pte_t *kpte, unsigned long address,
         * protection requirement in the large page.
         */
        new_prot = static_protections(req_prot, lpaddr, old_pfn, numpages,
-                                     CPA_DETECT);
+                                     psize, CPA_DETECT);
 
        /*
         * If there is a conflict, split the large page.
@@ -906,7 +914,8 @@ static void split_set_pte(struct cpa_data *cpa, pte_t *pte, unsigned long pfn,
        if (!cpa->force_static_prot)
                goto set;
 
-       prot = static_protections(ref_prot, address, pfn, npg, CPA_PROTECT);
+       /* Hand in lpsize = 0 to enforce the protection mechanism */
+       prot = static_protections(ref_prot, address, pfn, npg, 0, CPA_PROTECT);
 
        if (pgprot_val(prot) == pgprot_val(ref_prot))
                goto set;
@@ -1503,7 +1512,8 @@ repeat:
                pgprot_val(new_prot) |= pgprot_val(cpa->mask_set);
 
                cpa_inc_4k_install();
-               new_prot = static_protections(new_prot, address, pfn, 1,
+               /* Hand in lpsize = 0 to enforce the protection mechanism */
+               new_prot = static_protections(new_prot, address, pfn, 1, 0,
                                              CPA_PROTECT);
 
                new_prot = pgprot_clear_protnone_bits(new_prot);