[PATCH 2/2] mm: Abstract moving to the next PFN

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

In order to fix the L1TF vulnerability, x86 can invert the PTE bits for
PROT_NONE VMAs, which means we cannot move from one PTE to the next by
adding 1 to the PFN field of the PTE.  Abstract advancing the PTE to
the next PFN through a pte_next_pfn() function/macro.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Fixes: bcc6cc832573 ("mm: add default definition of set_ptes()")
Reported-by: syzbot+55cc72f8cc3a549119df@syzkaller.appspotmail.com
---
 arch/x86/include/asm/pgtable.h |  8 ++++++++
 include/linux/pgtable.h        | 10 +++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index d6ad98ca1288..e02b179ec659 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -955,6 +955,14 @@ static inline int pte_same(pte_t a, pte_t b)
 	return a.pte == b.pte;
 }
 
+static inline pte_t pte_next_pfn(pte_t pte)
+{
+	if (__pte_needs_invert(pte_val(pte)))
+		return __pte(pte_val(pte) - (1UL << PFN_PTE_SHIFT));
+	return __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT));
+}
+#define pte_next_pfn	pte_next_pfn
+
 static inline int pte_present(pte_t a)
 {
 	return pte_flags(a) & (_PAGE_PRESENT | _PAGE_PROTNONE);
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 1fba072b3dac..af7639c3b0a3 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -206,6 +206,14 @@ static inline int pmd_young(pmd_t pmd)
 #endif
 
 #ifndef set_ptes
+
+#ifndef pte_next_pfn
+static inline pte_t pte_next_pfn(pte_t pte)
+{
+	return __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT));
+}
+#endif
+
 /**
  * set_ptes - Map consecutive pages to a contiguous range of addresses.
  * @mm: Address space to map the pages into.
@@ -231,7 +239,7 @@ static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
 		if (--nr == 0)
 			break;
 		ptep++;
-		pte = __pte(pte_val(pte) + (1UL << PFN_PTE_SHIFT));
+		pte = pte_next_pfn(pte);
 	}
 	arch_leave_lazy_mmu_mode();
 }
-- 
2.40.1