The MPX code in the kernel needs to walk these tables in order to
populate them on demand as well as unmap them when memory is
freed. A larger virtual address space means larger MPX bounds
tables.
Update the bounds table walking code to understand how to walk
the larger table size. We use the new per-mm "mpx_bd_shift"
value to determine which format to use.
The mpx_bd_size_shift() function looks like a useless abstraction
here. But, the new 'mpx_bd_shift' field will get packed into a
single bit in 'bd_addr' later. Keep the abstraction in place now
to make the series simpler and make it more obvious when the
complexity comes from the packing rather than the actual data
etself.
---
b/arch/x86/include/asm/mpx.h | 27 +++++++++++++++++++++------
b/arch/x86/mm/mpx.c | 30 ++++++++++++++++++++++--------
2 files changed, 43 insertions(+), 14 deletions(-)
diff -puN arch/x86/include/asm/mpx.h~mawa-030-bounds-directory-sizes arch/x86/include/asm/mpx.h
--- a/arch/x86/include/asm/mpx.h~mawa-030-bounds-directory-sizes 2017-02-01 15:12:16.114142809 -0800
+++ b/arch/x86/include/asm/mpx.h 2017-02-01 15:12:16.119143034 -0800
@@ -14,15 +14,30 @@
#define MPX_BD_ENTRY_VALID_FLAG 0x1
/*
- * The upper 28 bits [47:20] of the virtual address in 64-bit
- * are used to index into bounds directory (BD).
+ * The uppermost bits [56:20] of the virtual address in 64-bit
+ * are used to index into bounds directory (BD). On processors
+ * with support for smaller virtual address space size, the "56"
+ * is obviously smaller.
*
- * The directory is 2G (2^31) in size, and with 8-byte entries
- * it has 2^28 entries.
+ * When using 47-bit virtual addresses, the directory is 2G
+ * (2^31) bytes in size, and with 8-byte entries it has 2^28
+ * entries. With 56-bit virtual addresses, it goes to 1T in size
+ * and has 2^37 entries.
+ *
+ * Needs to be ULL so we can use this in 32-bit kernels without
+ * warnings.
*/
-#define MPX_BD_SIZE_BYTES_64 (1UL<<31)
+#define MPX_BD_BASE_SIZE_BYTES_64 (1ULL<<31)
#define MPX_BD_ENTRY_BYTES_64 8
-#define MPX_BD_NR_ENTRIES_64 (MPX_BD_SIZE_BYTES_64/MPX_BD_ENTRY_BYTES_64)
+/*
+ * Note: size of tables on 64-bit is not constant, so we have no
+ * fixed definition for MPX_BD_NR_ENTRIES_64.
+ *
+ * The 5-Level Paging Whitepaper says: "A bound directory
+ * comprises 2^(28+MAWA) 64-bit entries." Since MAWA=0 in
+ * legacy mode:
+ */
+#define MPX_BD_LEGACY_NR_ENTRIES_64 (1UL<<28)
/*
* The 32-bit directory is 4MB (2^22) in size, and with 4-byte
diff -puN arch/x86/mm/mpx.c~mawa-030-bounds-directory-sizes arch/x86/mm/mpx.c
--- a/arch/x86/mm/mpx.c~mawa-030-bounds-directory-sizes 2017-02-01 15:12:16.115142854 -0800
+++ b/arch/x86/mm/mpx.c 2017-02-01 15:12:16.119143034 -0800
@@ -20,12 +20,21 @@
#define CREATE_TRACE_POINTS
#include <asm/trace/mpx.h>
+static inline int mpx_bd_size_shift(struct mm_struct *mm)
+{
+ return mm->context.mpx_bd_shift;
+}
+
static inline unsigned long mpx_bd_size_bytes(struct mm_struct *mm)
{
- if (is_64bit_mm(mm))
- return MPX_BD_SIZE_BYTES_64;
- else
+ if (!is_64bit_mm(mm))
return MPX_BD_SIZE_BYTES_32;
+
+ /*
+ * The bounds directory grows with the address space size.
+ * The "legacy" shift is 0.
+ */
+ return MPX_BD_BASE_SIZE_BYTES_64 << mpx_bd_shift_shift(mm);
}
static inline unsigned long mpx_bt_size_bytes(struct mm_struct *mm)
@@ -724,6 +733,7 @@ static inline unsigned long bd_entry_vir
{
unsigned long long virt_space;
unsigned long long GB = (1ULL << 30);
+ unsigned long legacy_64bit_vaddr_bits = 48;
/*
* This covers 32-bit emulation as well as 32-bit kernels
@@ -733,12 +743,16 @@ static inline unsigned long bd_entry_vir
return (4ULL * GB) / MPX_BD_NR_ENTRIES_32;
/*
- * 'x86_virt_bits' returns what the hardware is capable
- * of, and returns the full >32-bit address space when
- * running 32-bit kernels on 64-bit hardware.
+ * With 5-level paging, the virtual address space size
+ * gets bigger. A bounds directory entry still points to
+ * a single bounds table and the *tables* stay the same
+ * size. Thus, the address space that a directory entry
+ * covers does not change based on the paging mode or the
+ * size of the bounds directory itself. Just use the
+ * legacy size.
*/
- virt_space = (1ULL << boot_cpu_data.x86_virt_bits);
- return virt_space / MPX_BD_NR_ENTRIES_64;
+ virt_space = (1ULL << legacy_64bit_vaddr_bits);
+ return virt_space / MPX_BD_LEGACY_NR_ENTRIES_64;
}
/*
_
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
