ARM: shmobile: Move written variables from .text to .data

shmobile_scu_base is being written to, so it doesn't belong in the .text section. Fix this by moving it from asm .text to C .data, as it's no longer used from asm code since commit 4f6da36f7edd5790 ("ARM: shmobile:
Remove old SCU boot code").

Signed-off-by Geert Uytterhoeven <[email protected]>

Quoted 9 lines

arch/arm/mach-shmobile/platsmp-scu.c +0 -0

index 64663110ab6ca0e1..f2198c9c74359736 100644
@@ -17,6 +17,9 @@
  #include <asm/smp_scu.h>
  #include "common.h"
 

arch/arm/mach-shmobile/platsmp-scu.c line 20

Quoted 1 line

arch/arm/mach-shmobile/platsmp-scu.c +1 -0

+

Why add 2nd empty line?

When CONFIG_ARM_KERNMEM_PERMS=y and CONFIG_DEBUG_RODATA=y, the kernel crashes during system suspend:

Freezing user space processes ... (elapsed 0.004 seconds) done. Freezing remaining freezable tasks ... (elapsed 0.002 seconds) done.
PM: suspend of devices complete after 111.948 msecs
PM: late suspend of devices complete after 1.086 msecs
PM: noirq suspend of devices complete after 11.576 msecs Disabling non-boot CPUs ...
Kernel panic - not syncing: Attempted to kill the idle task! 1014ec ---[ end Kernel panic - not syncing: Attempted to kill the idle task!
CPU0: stopping

This happens because the .text section is marked read-only, while the arrays shmobile_smp_mpidr[], shmobile_smp_fn[], and shmobile_smp_arg[] are being written to.

Fix this by moving these arrays from the .text to the .data section. This requires accessing them through a pointer after virtual to physical translation.

Signed-off-by Geert Uytterhoeven <[email protected]>

---
 arch/arm/mach-shmobile/headsmp.S | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

arch/arm/mach-shmobile/headsmp.S +0 -0

index 330c1fc63197df89..f924273ceaf476b4 100644
@@ -50,9 +50,12 @@ ENTRY(shmobile_smp_boot)
 	mrc	p15, 0, r1, c0, c0, 5		@ r1 = MPIDR
 	and	r0, r1, r0			@ r0 = cpu_logical_map() value

Hi Simon, Magnus,

When CONFIG_ARM_KERNMEM_PERMS=y and CONFIG_DEBUG_RODATA=y, the kernel crashes during system suspend:

Freezing user space processes ... (elapsed 0.004 seconds) done. Freezing remaining freezable tasks ... (elapsed 0.002 seconds) done.
PM: suspend of devices complete after 111.948 msecs
PM: late suspend of devices complete after 1.086 msecs
PM: noirq suspend of devices complete after 11.576 msecs Disabling non-boot CPUs ...
Kernel panic - not syncing: Attempted to kill the idle task! 1014ec ---[ end Kernel panic - not syncing: Attempted to kill the idle task!
CPU0: stopping

This happens because the shmobile assembler sources have several variables that are written to in the .text section, while .text is mapped read-only after kernel bootup if CONFIG_DEBUG_RODATA=y.

This series fixes this by moving variables from .text to .data. Note that there's still an issue with shmobile_boot_fn and shmobile_boot_arg in arch/arm/mach-shmobile/headsmp.S.
So far I didn't manage to fix this (the code and data are copied to SRAM on some SoCs). However, currently this are harmless, as these are written during early kernel boot up only, before .text is marked read-only.

These issues were uncovered by "[PATCH v2] ARM: mm: flip priority of CONFIG_DEBUG_RODATA". As that patch is planned for queue up (again) soon, it may be a good idea to queue these fixes for v4.5, to avoid a dependency with the arm tree.

Tested hard on sh73a0/kzm9g, r8a7791/koelsch.
Tested lighter on emev2/kzm9d[*], r8a73a4/ape6evm, r8a7740/armadillo, and r8a7779/marzen[*] ([*] = no remote resume).

Thanks!

Geert Uytterhoeven (2):
ARM: shmobile: Move shmobile_scu_base from .text to .data
ARM: shmobile: Move shmobile_smp_{mpidr,fn,arg}[] from .text to .data

 arch/arm/mach-shmobile/headsmp-scu.S |  6 ------
 arch/arm/mach-shmobile/headsmp.S     | 22 ++++++++++++++++------
 arch/arm/mach-shmobile/platsmp-scu.c |  3 +++
 3 files changed, 19 insertions(+), 12 deletions(-)

--
1.9.1

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds

Quoted 39 lines · Geert Uytterhoeven

Hi Simon, Magnus,

When CONFIG_ARM_KERNMEM_PERMS=y and CONFIG_DEBUG_RODATA=y, the kernel crashes during system suspend:

Freezing user space processes ... (elapsed 0.004 seconds) done. Freezing remaining freezable tasks ... (elapsed 0.002 seconds) done.
PM: suspend of devices complete after 111.948 msecs
PM: late suspend of devices complete after 1.086 msecs
PM: noirq suspend of devices complete after 11.576 msecs Disabling non-boot CPUs ...
Kernel panic - not syncing: Attempted to kill the idle task! 1014ec ---[ end Kernel panic - not syncing: Attempted to kill the idle task!
CPU0: stopping

This happens because the shmobile assembler sources have several variables that are written to in the .text section, while .text is mapped read-only after kernel bootup if CONFIG_DEBUG_RODATA=y.

This series fixes this by moving variables from .text to .data. Note that there's still an issue with shmobile_boot_fn and shmobile_boot_arg in arch/arm/mach-shmobile/headsmp.S.
So far I didn't manage to fix this (the code and data are copied to SRAM on some SoCs). However, currently this are harmless, as these are written during early kernel boot up only, before .text is marked read-only.

These issues were uncovered by "[PATCH v2] ARM: mm: flip priority of CONFIG_DEBUG_RODATA". As that patch is planned for queue up (again) soon, it may be a good idea to queue these fixes for v4.5, to avoid a dependency with the arm tree.

Tested hard on sh73a0/kzm9g, r8a7791/koelsch.
Tested lighter on emev2/kzm9d[*], r8a73a4/ape6evm, r8a7740/armadillo, and r8a7779/marzen[*] ([*] = no remote resume).

Thanks!

Quoted 8 lines

Geert Uytterhoeven (2):
ARM: shmobile: Move shmobile_scu_base from .text to .data
ARM: shmobile: Move shmobile_smp_{mpidr,fn,arg}[] from .text to .data

 arch/arm/mach-shmobile/headsmp-scu.S |  6 ------
 arch/arm/mach-shmobile/headsmp.S     | 22 ++++++++++++++++------
 arch/arm/mach-shmobile/platsmp-scu.c |  3 +++
 3 files changed, 19 insertions(+), 12 deletions(-)

Thanks!

Reviewed-by Kees Cook <[email protected]>

And FWIW, I've now got the RODATA patch back in the patch queue, since we're at -rc1:
http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=8501/1

Quoted 4 lines · Kees Cook

And FWIW, I've now got the RODATA patch back in the patch queue, since we're at -rc1:
http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=8501/1

And I'll be dropping it into linux-next for next week (iow, I'll commit it tomorrow.)

Unfortunately, -rc1 broke some platforms, so Olof's builder isn't going to get full coverage of it while building only my tree.