x86/mm: Ignore A/D bits in pte/pmd/pud_none()

The erratum we are fixing here can lead to stray setting of the
A and D bits.  That means that a pte that we cleared might
suddenly have A/D set.  So, stop considering those bits when
determining if a pte is pte_none().  The same goes for the
other pmd_none() and pud_none().  pgd_none() can be skipped
because it is not affected; we do not use PGD entries for
anything other than pagetables on affected configurations.

This adds a tiny amount of overhead to all pte_none() checks.
I doubt we'll be able to measure it anywhere.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: dave.hansen@intel.com
Cc: linux-mm@kvack.org
Cc: mhocko@suse.com
Link: http://lkml.kernel.org/r/20160708001912.5216F89C@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/pgtable.h

@@ -480,7 +480,7 @@ pte_t *populate_extra_pte(unsigned long vaddr);
 
 static inline int pte_none(pte_t pte)
 {
-	return !pte.pte;
+	return !(pte.pte & ~(_PAGE_KNL_ERRATUM_MASK));
 }
 
 #define __HAVE_ARCH_PTE_SAME
@@ -552,7 +552,8 @@ static inline int pmd_none(pmd_t pmd)
 {
 	/* Only check low word on 32-bit platforms, since it might be
 	   out of sync with upper half. */
-	return (unsigned long)native_pmd_val(pmd) == 0;
+	unsigned long val = native_pmd_val(pmd);
+	return (val & ~_PAGE_KNL_ERRATUM_MASK) == 0;
 }
 
 static inline unsigned long pmd_page_vaddr(pmd_t pmd)
@@ -616,7 +617,7 @@ static inline unsigned long pages_to_mb(unsigned long npg)
 #if CONFIG_PGTABLE_LEVELS > 2
 static inline int pud_none(pud_t pud)
 {
-	return native_pud_val(pud) == 0;
+	return (native_pud_val(pud) & ~(_PAGE_KNL_ERRATUM_MASK)) == 0;
 }
 
 static inline int pud_present(pud_t pud)
@@ -694,6 +695,12 @@ static inline int pgd_bad(pgd_t pgd)
 
 static inline int pgd_none(pgd_t pgd)
 {
+	/*
+	 * There is no need to do a workaround for the KNL stray
+	 * A/D bit erratum here.  PGDs only point to page tables
+	 * except on 32-bit non-PAE which is not supported on
+	 * KNL.
+	 */
 	return !native_pgd_val(pgd);
 }
 #endif	/* CONFIG_PGTABLE_LEVELS > 3 */

arch/x86/include/asm/pgtable_types.h

@@ -70,6 +70,12 @@
 			 _PAGE_PKEY_BIT2 | \
 			 _PAGE_PKEY_BIT3)
 
+#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
+#define _PAGE_KNL_ERRATUM_MASK (_PAGE_DIRTY | _PAGE_ACCESSED)
+#else
+#define _PAGE_KNL_ERRATUM_MASK 0
+#endif
+
 #ifdef CONFIG_KMEMCHECK
 #define _PAGE_HIDDEN	(_AT(pteval_t, 1) << _PAGE_BIT_HIDDEN)
 #else