arch/x86/include/asm/pgtable-invert.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _ASM_PGTABLE_INVERT_H
   3 #define _ASM_PGTABLE_INVERT_H 1
   4
   5 #ifndef __ASSEMBLY__
   6
   7 /*
   8  * A clear pte value is special, and doesn't get inverted.
   9  *
  10  * Note that even users that only pass a pgprot_t (rather
  11  * than a full pte) won't trigger the special zero case,
  12  * because even PAGE_NONE has _PAGE_PROTNONE | _PAGE_ACCESSED
  13  * set. So the all zero case really is limited to just the
  14  * cleared page table entry case.
  15  */
  16 static inline bool __pte_needs_invert(u64 val)
  17 {
  18         return val && !(val & _PAGE_PRESENT);
  19 }
  20
  21 /* Get a mask to xor with the page table entry to get the correct pfn. */
  22 static inline u64 protnone_mask(u64 val)
  23 {
  24         return __pte_needs_invert(val) ?  ~0ull : 0;
  25 }
  26
  27 static inline u64 flip_protnone_guard(u64 oldval, u64 val, u64 mask)
  28 {
  29         /*
  30          * When a PTE transitions from NONE to !NONE or vice-versa
  31          * invert the PFN part to stop speculation.
  32          * pte_pfn undoes this when needed.
  33          */
  34         if (__pte_needs_invert(oldval) != __pte_needs_invert(val))
  35                 val = (val & ~mask) | (~val & mask);
  36         return val;
  37 }
  38
  39 #endif /* __ASSEMBLY__ */
  40
  41 #endif