arm/module: maximum utilization of module area.

This patch defines new macro MODULE_START to ensure kernel text
and module remains within 32 MB of address range.

Tried this patch by inserting 20 MB size module on 4.1 kernel:-

Earlier:-
==========
sh# insmod size.ko
....
insmod: ERROR: could not insert module size.ko: Cannot allocate memory
sh#

With this patch
===============
sh# insmod size.ko
...
sh# lsmod
Module                  Size  Used by
size                20972425  0

Signed-off-by: Vaneet Narang <redacted>
Signed-off-by: Maninder Singh <redacted>
Reviewed-by: Ajeet Yadav <redacted>
---
 arch/arm/include/asm/memory.h | 4 ++--
 arch/arm/kernel/module.c      | 9 ++++++++-
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index 76cbd9c..1a0a6e5 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h

@@ -37,7 +37,7 @@
  * TASK_SIZE - the maximum size of a user space task.
  * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area
  */
-#define TASK_SIZE		(UL(CONFIG_PAGE_OFFSET) - UL(SZ_16M))
+#define TASK_SIZE		(UL(CONFIG_PAGE_OFFSET) - UL(SZ_32M))
 #define TASK_UNMAPPED_BASE	ALIGN(TASK_SIZE / 3, SZ_16M)
 
 /*

@@ -50,7 +50,7 @@
  * and PAGE_OFFSET - it must be within 32MB of the kernel text.
  */
 #ifndef CONFIG_THUMB2_KERNEL
-#define MODULES_VADDR		(PAGE_OFFSET - SZ_16M)
+#define MODULES_VADDR		(PAGE_OFFSET - SZ_32M)
 #else
 /* smaller range for Thumb-2 symbols relocation (2^24)*/
 #define MODULES_VADDR		(PAGE_OFFSET - SZ_8M)

diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
index 4f14b5c..b8e1f9c 100644
--- a/arch/arm/kernel/module.c
+++ b/arch/arm/kernel/module.c

@@ -35,12 +35,19 @@
  */
 #undef MODULES_VADDR
 #define MODULES_VADDR	(((unsigned long)_exiprom + ~PMD_MASK) & PMD_MASK)
+#define MODULES_START MODULES_VADDR
+#else
+#ifndef CONFIG_THUMB2_KERNEL
+#define MODULES_START  ALIGN((unsigned long)_etext - SZ_32M, PAGE_SIZE)
+#else
+#define MODULES_START MODULES_VADDR
+#endif
 #endif
 
 #ifdef CONFIG_MMU
 void *module_alloc(unsigned long size)
 {
-	void *p = __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END,
+	void *p = __vmalloc_node_range(size, 1, MODULES_START, MODULES_END,
 				GFP_KERNEL, PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
 				__builtin_return_address(0));
 	if (!IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || p)

-- 
1.9.1

On 6 December 2016 at 08:29, Maninder Singh [off-list ref] wrote:

22 more quoted lines

On a multi_v7_defconfig kernel, the text size is >8 MB, which means
you are only adding ~7 MB to the module area, while consuming 16 MB of
additional address space. Given that 20 MB modules are very uncommon,
I think it is better to enable CONFIG_ARM_MODULE_PLTS instead. That
way, there is no need to update these defaults for everyone.

+#else
+#define MODULES_START MODULES_VADDR
+#endif
 #endif

 #ifdef CONFIG_MMU
 void *module_alloc(unsigned long size)
 {
-       void *p = __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END,
+       void *p = __vmalloc_node_range(size, 1, MODULES_START, MODULES_END,
                                GFP_KERNEL, PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
                                __builtin_return_address(0));
        if (!IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || p)
--
1.9.1


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On Tue, 6 Dec 2016, Maninder Singh wrote:

This patch defines new macro MODULE_START to ensure kernel text
and module remains within 32 MB of address range.

Tried this patch by inserting 20 MB size module on 4.1 kernel:-

Earlier:-
==========
sh# insmod size.ko
....
insmod: ERROR: could not insert module size.ko: Cannot allocate memory
sh#

With this patch
===============
sh# insmod size.ko
...
sh# lsmod
Module                  Size  Used by
size                20972425  0

Could you please try enabling CONFIG_ARM_MODULE_PLTS instead of this 
patch?


Nicolas

On Tue, Dec 06, 2016 at 01:59:35PM +0530, Maninder Singh wrote:

This patch defines new macro MODULE_START to ensure kernel text
and module remains within 32 MB of address range.

Tried this patch by inserting 20 MB size module on 4.1 kernel:-

Earlier:-
==========
sh# insmod size.ko
....
insmod: ERROR: could not insert module size.ko: Cannot allocate memory
sh#

With this patch
===============
sh# insmod size.ko
...
sh# lsmod
Module                  Size  Used by
size                20972425  0

Signed-off-by: Vaneet Narang <redacted>
Signed-off-by: Maninder Singh <redacted>
Reviewed-by: Ajeet Yadav <redacted>

A PC24 relocation has a range of +/-32MB.  This means that where-ever
the module is placed, it must be capable of reaching any function
within the kernel text, which may itself be quite large (eg, 8MB, or
possibly larger).  The module area exists to allow modules to be
located in an area where PC24 relocations are able to reach all of the
kernel text on sensibly configured kernels, thereby allowing for
optimal performance.

If you wish to load large modules, then enable ARM_MODULE_PLTS, which
will use the less efficient PLT method (which is basically an indirect
function call) for relocations that PC24 can't handle, and will allow
the module to be loaded into the vmalloc area.

Growing the module area so that smaller modules also get penalised by
the PLT indirection is not sane.

So, I'm afraid this change is not acceptable.

-- 
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