riscv: Add pte bit to distinguish swap from invalid

sorear · palmer-dabbelt · commit e3613bb8afc2 · 2019-02-11T15:24:45.000-08:00
Previously, invalid PTEs and swap PTEs had the same binary
representation, causing errors when attempting to unmap PROT_NONE
mappings, including implicit unmap on exit.

Typical error:

swap_info_get: Bad swap file entry 40000000007a9879
BUG: Bad page map in process a.out  pte:3d4c3cc0 pmd:3e521401

Cc: stable@vger.kernel.org
Signed-off-by: Stefan O'Rear &lt;sorear2@gmail.com&gt;
Reviewed-by: Christoph Hellwig &lt;hch@lst.de&gt;
Signed-off-by: Palmer Dabbelt &lt;palmer@sifive.com&gt;
diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
@@ -35,6 +35,12 @@
 #define _PAGE_SPECIAL   _PAGE_SOFT
 #define _PAGE_TABLE     _PAGE_PRESENT
 
+/*
+ * _PAGE_PROT_NONE is set on not-present pages (and ignored by the hardware) to
+ * distinguish them from swapped out pages
+ */
+#define _PAGE_PROT_NONE _PAGE_READ
+
 #define _PAGE_PFN_SHIFT 10
 
 /* Set of bits to preserve across pte_modify() */
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
@@ -44,7 +44,7 @@
 /* Page protection bits */
 #define _PAGE_BASE	(_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_USER)
 
-#define PAGE_NONE		__pgprot(0)
+#define PAGE_NONE		__pgprot(_PAGE_PROT_NONE)
 #define PAGE_READ		__pgprot(_PAGE_BASE | _PAGE_READ)
 #define PAGE_WRITE		__pgprot(_PAGE_BASE | _PAGE_READ | _PAGE_WRITE)
 #define PAGE_EXEC		__pgprot(_PAGE_BASE | _PAGE_EXEC)
@@ -98,7 +98,7 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 
 static inline int pmd_present(pmd_t pmd)
 {
-	return (pmd_val(pmd) & _PAGE_PRESENT);
+	return (pmd_val(pmd) & (_PAGE_PRESENT | _PAGE_PROT_NONE));
 }
 
 static inline int pmd_none(pmd_t pmd)
@@ -178,7 +178,7 @@ static inline pte_t *pte_offset_kernel(pmd_t *pmd, unsigned long addr)
 
 static inline int pte_present(pte_t pte)
 {
-	return (pte_val(pte) & _PAGE_PRESENT);
+	return (pte_val(pte) & (_PAGE_PRESENT | _PAGE_PROT_NONE));
 }
 
 static inline int pte_none(pte_t pte)
@@ -380,7 +380,7 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
  *
  * Format of swap PTE:
  *	bit            0:	_PAGE_PRESENT (zero)
- *	bit            1:	reserved for future use (zero)
+ *	bit            1:	_PAGE_PROT_NONE (zero)
  *	bits      2 to 6:	swap type
  *	bits 7 to XLEN-1:	swap offset
  */

Original file line number	Diff line number	Diff line change
`@@ -44,7 +44,7 @@`
`44`	`44`	`/* Page protection bits */`
`45`	`45`	`#define _PAGE_BASE (_PAGE_PRESENT \| _PAGE_ACCESSED \| _PAGE_USER)`
`46`	`46`
`47`		`-#define PAGE_NONE __pgprot(0)`
	`47`	`+#define PAGE_NONE __pgprot(_PAGE_PROT_NONE)`
`48`	`48`	`#define PAGE_READ __pgprot(_PAGE_BASE \| _PAGE_READ)`
`49`	`49`	`#define PAGE_WRITE __pgprot(_PAGE_BASE \| _PAGE_READ \| _PAGE_WRITE)`
`50`	`50`	`#define PAGE_EXEC __pgprot(_PAGE_BASE \| _PAGE_EXEC)`
`@@ -98,7 +98,7 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];`
`98`	`98`
`99`	`99`	`static inline int pmd_present(pmd_t pmd)`
`100`	`100`	`{`
`101`		`- return (pmd_val(pmd) & _PAGE_PRESENT);`
	`101`	`+ return (pmd_val(pmd) & (_PAGE_PRESENT \| _PAGE_PROT_NONE));`
`102`	`102`	`}`
`103`	`103`
`104`	`104`	`static inline int pmd_none(pmd_t pmd)`
`@@ -178,7 +178,7 @@ static inline pte_t pte_offset_kernel(pmd_t pmd, unsigned long addr)`
`178`	`178`
`179`	`179`	`static inline int pte_present(pte_t pte)`
`180`	`180`	`{`
`181`		`- return (pte_val(pte) & _PAGE_PRESENT);`
	`181`	`+ return (pte_val(pte) & (_PAGE_PRESENT \| _PAGE_PROT_NONE));`
`182`	`182`	`}`
`183`	`183`
`184`	`184`	`static inline int pte_none(pte_t pte)`
`@@ -380,7 +380,7 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,`
`380`	`380`	`*`
`381`	`381`	`* Format of swap PTE:`
`382`	`382`	`* bit 0: _PAGE_PRESENT (zero)`
`383`		`- * bit 1: reserved for future use (zero)`
	`383`	`+ * bit 1: _PAGE_PROT_NONE (zero)`
`384`	`384`	`* bits 2 to 6: swap type`
`385`	`385`	`* bits 7 to XLEN-1: swap offset`
`386`	`386`	`*/`