From: Stefan O'Rear <sorear2@gmail.com>
To: Palmer Dabbelt <palmer@sifive.com>,
Albert Ou <aou@eecs.berkeley.edu>,
linux-riscv@lists.infradead.org
Cc: Stefan O'Rear <sorear2@gmail.com>, schwab@suse.de
Subject: [PATCH] riscv: Add pte bit to distinguish swap from invalid
Date: Sun, 16 Dec 2018 13:03:36 -0500 [thread overview]
Message-ID: <1544983416-32532-1-git-send-email-sorear2@gmail.com> (raw)
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 <sorear2@gmail.com>
---
arch/riscv/include/asm/pgtable-bits.h | 6 ++++++
arch/riscv/include/asm/pgtable.h | 8 ++++----
2 files changed, 10 insertions(+), 4 deletions(-)
Reproducer:
#include <sys/mman.h>
int
main (void)
{
char *a = mmap (0, 4096, PROT_READ | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
++*a;
mprotect (a, 4096, PROT_NONE);
}
diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h
index 2fa2942..470755c 100644
--- 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
index 1630196..a8179a8 100644
--- 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
*/
--
2.8.0
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next reply other threads:[~2018-12-16 18:04 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-16 18:03 Stefan O'Rear [this message]
2018-12-17 18:37 ` [PATCH] riscv: Add pte bit to distinguish swap from invalid Christoph Hellwig
2019-02-08 17:36 ` David Abdurachmanov
2019-02-08 17:46 ` Palmer Dabbelt
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