MIPS: Make TASK_SIZE reflect proper size for both 32 and 64 bit processes.

The TASK_SIZE macro should reflect the size of a user process virtual
address space.  Previously for 64-bit kernels, this was not the case.
The immediate cause of pain was in
hugetlbfs/inode.c:hugetlb_get_unmapped_area() where 32-bit processes
trying to mmap a huge page would be served a page with an address
outside of the 32-bit address range.  But there are other uses of
TASK_SIZE in the kernel as well that would like an accurate value.

The new definition is nice because it now makes TASK_SIZE and
TASK_SIZE_OF() yield the same value for any given process.

For 32-bit kernels there should be no change, although I did factor
out some code in asm/processor.h that became identical for the 32-bit and
64-bit cases.

__UA_LIMIT is now set to ~((1 << SEGBITS) - 1) for 64-bit kernels.
This should eliminate the possibility of getting a
AddressErrorException in the kernel for addresses that pass the
access_ok() test.

With the patch applied, I can still run o32, n32 and n64 processes,
and have an o32 shell fork/exec both n32 and n64 processes.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1701/

1 files changed, 19 insertions, 21 deletions

diff --git a/arch/mips/include/asm/processor.h b/arch/mips/include/asm/processor.h
index 0d629bb93cbe..ead6928fa6b8 100644
--- a/arch/mips/include/asm/processor.h
+++ b/arch/mips/include/asm/processor.h
@@ -50,13 +50,10 @@ extern unsigned int vced_count, vcei_count;
  * so don't change it unless you know what you are doing.
  */
 #define TASK_SIZE	0x7fff8000UL
-#define STACK_TOP	((TASK_SIZE & PAGE_MASK) - SPECIAL_PAGES_SIZE)
 
-/*
- * This decides where the kernel will search for a free chunk of vm
- * space during mmap's.
- */
-#define TASK_UNMAPPED_BASE	((TASK_SIZE / 3) & ~(PAGE_SIZE))
+#ifdef __KERNEL__
+#define STACK_TOP_MAX	TASK_SIZE
+#endif
 
 #define TASK_IS_32BIT_ADDR 1
 
@@ -71,28 +68,29 @@ extern unsigned int vced_count, vcei_count;
  * 8192EB ...
  */
 #define TASK_SIZE32	0x7fff8000UL
-#define TASK_SIZE	0x10000000000UL
-#define STACK_TOP	\
-	(((test_thread_flag(TIF_32BIT_ADDR) ?				\
-	   TASK_SIZE32 : TASK_SIZE) & PAGE_MASK) - SPECIAL_PAGES_SIZE)
+#define TASK_SIZE64	0x10000000000UL
+#define TASK_SIZE (test_thread_flag(TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE64)
+
+#ifdef __KERNEL__
+#define STACK_TOP_MAX	TASK_SIZE64
+#endif
+
 
-/*
- * This decides where the kernel will search for a free chunk of vm
- * space during mmap's.
- */
-#define TASK_UNMAPPED_BASE						\
-	(test_thread_flag(TIF_32BIT_ADDR) ?				\
-		PAGE_ALIGN(TASK_SIZE32 / 3) : PAGE_ALIGN(TASK_SIZE / 3))
 #define TASK_SIZE_OF(tsk)						\
-	(test_tsk_thread_flag(tsk, TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE)
+	(test_tsk_thread_flag(tsk, TIF_32BIT_ADDR) ? TASK_SIZE32 : TASK_SIZE64)
 
 #define TASK_IS_32BIT_ADDR test_thread_flag(TIF_32BIT_ADDR)
 
 #endif
 
-#ifdef __KERNEL__
-#define STACK_TOP_MAX	TASK_SIZE
-#endif
+#define STACK_TOP	((TASK_SIZE & PAGE_MASK) - SPECIAL_PAGES_SIZE)
+
+/*
+ * This decides where the kernel will search for a free chunk of vm
+ * space during mmap's.
+ */
+#define TASK_UNMAPPED_BASE PAGE_ALIGN(TASK_SIZE / 3)
+
 
 #define NUM_FPU_REGS	32