* [PATCH 1/3] powerpc/modules: Load modules closer to kernel text
@ 2021-04-01 13:30 Christophe Leroy
2021-04-01 13:30 ` [PATCH 2/3] powerpc/8xx: Define a MODULE area below " Christophe Leroy
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Christophe Leroy @ 2021-04-01 13:30 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman, jniethe5
Cc: linux-kernel, linuxppc-dev
On book3s/32, when STRICT_KERNEL_RWX is selected, modules are
allocated on the segment just before kernel text, ie on the
0xb0000000-0xbfffffff when PAGE_OFFSET is 0xc0000000.
On the 8xx, TASK_SIZE is 0x80000000. The space between TASK_SIZE and
PAGE_OFFSET is not used and could be used for modules.
The idea comes from ARM architecture.
Having modules just below PAGE_OFFSET offers an opportunity to
minimise the distance between kernel text and modules and avoid
trampolines in modules to access kernel functions or other module
functions.
When MODULES_VADDR is defined, powerpc has it's own module_alloc()
function. In that function, first try to allocate the module
above the limit defined by '_etext - 32M'. Then if the allocation
fails, fallback to the entire MODULES area.
DEBUG logs in module_32.c without the patch:
[ 1572.588822] module_32: Applying ADD relocate section 13 to 12
[ 1572.588891] module_32: Doing plt for call to 0xc00671a4 at 0xcae04024
[ 1572.588964] module_32: Initialized plt for 0xc00671a4 at cae04000
[ 1572.589037] module_32: REL24 value = CAE04000. location = CAE04024
[ 1572.589110] module_32: Location before: 48000001.
[ 1572.589171] module_32: Location after: 4BFFFFDD.
[ 1572.589231] module_32: ie. jump to 03FFFFDC+CAE04024 = CEE04000
[ 1572.589317] module_32: Applying ADD relocate section 15 to 14
[ 1572.589386] module_32: Doing plt for call to 0xc00671a4 at 0xcadfc018
[ 1572.589457] module_32: Initialized plt for 0xc00671a4 at cadfc000
[ 1572.589529] module_32: REL24 value = CADFC000. location = CADFC018
[ 1572.589601] module_32: Location before: 48000000.
[ 1572.589661] module_32: Location after: 4BFFFFE8.
[ 1572.589723] module_32: ie. jump to 03FFFFE8+CADFC018 = CEDFC000
With the patch:
[ 279.404671] module_32: Applying ADD relocate section 13 to 12
[ 279.404741] module_32: REL24 value = C00671B4. location = BF808024
[ 279.404814] module_32: Location before: 48000001.
[ 279.404874] module_32: Location after: 4885F191.
[ 279.404933] module_32: ie. jump to 0085F190+BF808024 = C00671B4
[ 279.405016] module_32: Applying ADD relocate section 15 to 14
[ 279.405085] module_32: REL24 value = C00671B4. location = BF800018
[ 279.405156] module_32: Location before: 48000000.
[ 279.405215] module_32: Location after: 4886719C.
[ 279.405275] module_32: ie. jump to 0086719C+BF800018 = C00671B4
We see that with the patch, no plt entries are set.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/kernel/module.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
index a211b0253cdb..fab84024650c 100644
--- a/arch/powerpc/kernel/module.c
+++ b/arch/powerpc/kernel/module.c
@@ -14,6 +14,7 @@
#include <asm/firmware.h>
#include <linux/sort.h>
#include <asm/setup.h>
+#include <asm/sections.h>
static LIST_HEAD(module_bug_list);
@@ -88,12 +89,28 @@ int module_finalize(const Elf_Ehdr *hdr,
}
#ifdef MODULES_VADDR
+static __always_inline void *
+__module_alloc(unsigned long size, unsigned long start, unsigned long end)
+{
+ return __vmalloc_node_range(size, 1, start, end, GFP_KERNEL,
+ PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
+ __builtin_return_address(0));
+}
+
void *module_alloc(unsigned long size)
{
+ unsigned long limit = (unsigned long)_etext - SZ_32M;
+ void *ptr = NULL;
+
BUILD_BUG_ON(TASK_SIZE > MODULES_VADDR);
- return __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END, GFP_KERNEL,
- PAGE_KERNEL_EXEC, VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
- __builtin_return_address(0));
+ /* First try within 32M limit from _etext to avoid branch trampolines */
+ if (MODULES_VADDR < PAGE_OFFSET && MODULES_END > limit)
+ ptr = __module_alloc(size, limit, MODULES_END);
+
+ if (!ptr)
+ ptr = __module_alloc(size, MODULES_VADDR, MODULES_END);
+
+ return ptr;
}
#endif
--
2.25.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH 2/3] powerpc/8xx: Define a MODULE area below kernel text
2021-04-01 13:30 [PATCH 1/3] powerpc/modules: Load modules closer to kernel text Christophe Leroy
@ 2021-04-01 13:30 ` Christophe Leroy
2021-04-01 13:30 ` [PATCH 3/3] powerpc/32s: Define a MODULE area below kernel text all the time Christophe Leroy
2021-04-19 3:59 ` [PATCH 1/3] powerpc/modules: Load modules closer to kernel text Michael Ellerman
2 siblings, 0 replies; 4+ messages in thread
From: Christophe Leroy @ 2021-04-01 13:30 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman, jniethe5
Cc: linux-kernel, linuxppc-dev
On the 8xx, TASK_SIZE is 0x80000000. The space between TASK_SIZE
and PAGE_OFFSET is not used.
In order to benefit from the powerpc specific module_alloc()
function which allocate modules with 32 Mbytes from
end of kernel text, define MODULES_VADDR and MODULES_END.
Set a 256Mb area just below PAGE_OFFSET, like book3s/32.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/include/asm/nohash/32/mmu-8xx.h | 3 +++
1 file changed, 3 insertions(+)
diff --git a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
index 478249959baa..6e4faa0a9b35 100644
--- a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
+++ b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h
@@ -172,6 +172,9 @@
#define mmu_linear_psize MMU_PAGE_8M
+#define MODULES_VADDR (PAGE_OFFSET - SZ_256M)
+#define MODULES_END PAGE_OFFSET
+
#ifndef __ASSEMBLY__
#include <linux/mmdebug.h>
--
2.25.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH 3/3] powerpc/32s: Define a MODULE area below kernel text all the time
2021-04-01 13:30 [PATCH 1/3] powerpc/modules: Load modules closer to kernel text Christophe Leroy
2021-04-01 13:30 ` [PATCH 2/3] powerpc/8xx: Define a MODULE area below " Christophe Leroy
@ 2021-04-01 13:30 ` Christophe Leroy
2021-04-19 3:59 ` [PATCH 1/3] powerpc/modules: Load modules closer to kernel text Michael Ellerman
2 siblings, 0 replies; 4+ messages in thread
From: Christophe Leroy @ 2021-04-01 13:30 UTC (permalink / raw)
To: Benjamin Herrenschmidt, Paul Mackerras, Michael Ellerman, jniethe5
Cc: linux-kernel, linuxppc-dev
On book3s/32, the segment below kernel text is used for module
allocation when CONFIG_STRICT_KERNEL_RWX is defined.
In order to benefit from the powerpc specific module_alloc()
function which allocate modules with 32 Mbytes from
end of kernel text, use that segment below PAGE_OFFSET at all time.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/Kconfig | 2 +-
arch/powerpc/include/asm/book3s/32/pgtable.h | 2 --
arch/powerpc/mm/book3s32/mmu.c | 7 -------
3 files changed, 1 insertion(+), 10 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c1344c05226c..15a91202d5c3 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -1219,7 +1219,7 @@ config TASK_SIZE_BOOL
config TASK_SIZE
hex "Size of user task space" if TASK_SIZE_BOOL
default "0x80000000" if PPC_8xx
- default "0xb0000000" if PPC_BOOK3S_32 && STRICT_KERNEL_RWX
+ default "0xb0000000" if PPC_BOOK3S_32
default "0xc0000000"
endmenu
diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
index 415ae29fa73a..83c65845a1a9 100644
--- a/arch/powerpc/include/asm/book3s/32/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/32/pgtable.h
@@ -194,10 +194,8 @@ int map_kernel_page(unsigned long va, phys_addr_t pa, pgprot_t prot);
#define VMALLOC_END ioremap_bot
#endif
-#ifdef CONFIG_STRICT_KERNEL_RWX
#define MODULES_END ALIGN_DOWN(PAGE_OFFSET, SZ_256M)
#define MODULES_VADDR (MODULES_END - SZ_256M)
-#endif
#ifndef __ASSEMBLY__
#include <linux/sched.h>
diff --git a/arch/powerpc/mm/book3s32/mmu.c b/arch/powerpc/mm/book3s32/mmu.c
index a0db398b5c26..159930351d9f 100644
--- a/arch/powerpc/mm/book3s32/mmu.c
+++ b/arch/powerpc/mm/book3s32/mmu.c
@@ -184,17 +184,10 @@ static bool is_module_segment(unsigned long addr)
{
if (!IS_ENABLED(CONFIG_MODULES))
return false;
-#ifdef MODULES_VADDR
if (addr < ALIGN_DOWN(MODULES_VADDR, SZ_256M))
return false;
if (addr > ALIGN(MODULES_END, SZ_256M) - 1)
return false;
-#else
- if (addr < ALIGN_DOWN(VMALLOC_START, SZ_256M))
- return false;
- if (addr > ALIGN(VMALLOC_END, SZ_256M) - 1)
- return false;
-#endif
return true;
}
--
2.25.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH 1/3] powerpc/modules: Load modules closer to kernel text
2021-04-01 13:30 [PATCH 1/3] powerpc/modules: Load modules closer to kernel text Christophe Leroy
2021-04-01 13:30 ` [PATCH 2/3] powerpc/8xx: Define a MODULE area below " Christophe Leroy
2021-04-01 13:30 ` [PATCH 3/3] powerpc/32s: Define a MODULE area below kernel text all the time Christophe Leroy
@ 2021-04-19 3:59 ` Michael Ellerman
2 siblings, 0 replies; 4+ messages in thread
From: Michael Ellerman @ 2021-04-19 3:59 UTC (permalink / raw)
To: Paul Mackerras, Benjamin Herrenschmidt, jniethe5,
Christophe Leroy, Michael Ellerman
Cc: linuxppc-dev, linux-kernel
On Thu, 1 Apr 2021 13:30:41 +0000 (UTC), Christophe Leroy wrote:
> On book3s/32, when STRICT_KERNEL_RWX is selected, modules are
> allocated on the segment just before kernel text, ie on the
> 0xb0000000-0xbfffffff when PAGE_OFFSET is 0xc0000000.
>
> On the 8xx, TASK_SIZE is 0x80000000. The space between TASK_SIZE and
> PAGE_OFFSET is not used and could be used for modules.
>
> [...]
Applied to powerpc/next.
[1/3] powerpc/modules: Load modules closer to kernel text
https://git.kernel.org/powerpc/c/2ec13df167040cd153c25c4d96d0ffc573ac4c40
[2/3] powerpc/8xx: Define a MODULE area below kernel text
https://git.kernel.org/powerpc/c/9132a2e82adc6e5a1c7c7385df3bfb25576bdd80
[3/3] powerpc/32s: Define a MODULE area below kernel text all the time
https://git.kernel.org/powerpc/c/80edc68e0479bafdc4869ec3351e42316b824596
cheers
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-04-01 13:30 [PATCH 1/3] powerpc/modules: Load modules closer to kernel text Christophe Leroy
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2021-04-01 13:30 ` [PATCH 3/3] powerpc/32s: Define a MODULE area below kernel text all the time Christophe Leroy
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