[PATCH] [stable 3.18 through 4.4] ARM: 8452/3: PJ4: make coprocessor access sequences buildable in Thumb2 mode

[PATCH] [stable 3.18 through 4.4] ARM: 8452/3: PJ4: make coprocessor access sequences buildable in Thumb2 mode

[Arnd Bergmann]

From: Ard Biesheuvel <ard.biesheuvel@linaro.org>

Commit 5008efc83bf85b647aa1cbc44718b1675bbb7444 upstream.

The PJ4 inline asm sequence to write to cp15 cannot be built in Thumb-2
mode, due to the way it performs arithmetic on the program counter, so it
is built in ARM mode instead. However, building C files in ARM mode under
CONFIG_THUMB2_KERNEL is problematic, since the instrumentation performed
by subsystems like ftrace does not expect having to deal with interworking
branches.

Since the sequence in question is simply a poor man's ISB instruction,
let's use a straight 'isb' instead when building in Thumb2 mode. Thumb2
implies V7, so 'isb' should always be supported in that case.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
Hi Greg,

As Ard pointed out, commit 13d1b9575ac2c2da ("ARM: 8221/1: PJ4: allow
building in Thumb-2 mode") which I suggested for backports into
3.16 is broken unless we also take this one.

I checked the other stable branches and found that both 3.18 and
4.4 contain only the first of the two, so please apply this one on
both branches as well.

3.16 and contain neither patch at the moment, but I have added both
to my local 3.16 series.
---
 arch/arm/kernel/Makefile  | 1 -
 arch/arm/kernel/pj4-cp0.c | 4 ++++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 2ecc7d15bc09..03120e656aea 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -84,7 +84,6 @@ obj-$(CONFIG_CPU_PJ4B)		+= pj4-cp0.o
 obj-$(CONFIG_IWMMXT)		+= iwmmxt.o
 obj-$(CONFIG_PERF_EVENTS)	+= perf_regs.o
 obj-$(CONFIG_HW_PERF_EVENTS)	+= perf_event.o perf_event_cpu.o
-CFLAGS_pj4-cp0.o		:= -marm
 AFLAGS_iwmmxt.o			:= -Wa,-mcpu=iwmmxt
 obj-$(CONFIG_ARM_CPU_TOPOLOGY)  += topology.o
 
diff --git a/arch/arm/kernel/pj4-cp0.c b/arch/arm/kernel/pj4-cp0.c
index 8153e36b2491..7c9248b74d3f 100644
--- a/arch/arm/kernel/pj4-cp0.c
+++ b/arch/arm/kernel/pj4-cp0.c
@@ -66,9 +66,13 @@ static void __init pj4_cp_access_write(u32 value)
 
 	__asm__ __volatile__ (
 		"mcr	p15, 0, %1, c1, c0, 2\n\t"
+#ifdef CONFIG_THUMB2_KERNEL
+		"isb\n\t"
+#else
 		"mrc	p15, 0, %0, c1, c0, 2\n\t"
 		"mov	%0, %0\n\t"
 		"sub	pc, pc, #4\n\t"
+#endif
 		: "=r" (temp) : "r" (value));
 }
 
-- 
2.9.0

Re: [PATCH] [stable 3.18 through 4.4] ARM: 8452/3: PJ4: make coprocessor access sequences buildable in Thumb2 mode

[Arnd Bergmann]

On Mon, May 8, 2017 at 9:55 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>
> Commit 5008efc83bf85b647aa1cbc44718b1675bbb7444 upstream.
>
> The PJ4 inline asm sequence to write to cp15 cannot be built in Thumb-2
> mode, due to the way it performs arithmetic on the program counter, so it
> is built in ARM mode instead. However, building C files in ARM mode under
> CONFIG_THUMB2_KERNEL is problematic, since the instrumentation performed
> by subsystems like ftrace does not expect having to deal with interworking
> branches.
>
> Since the sequence in question is simply a poor man's ISB instruction,
> let's use a straight 'isb' instead when building in Thumb2 mode. Thumb2
> implies V7, so 'isb' should always be supported in that case.
>
> Acked-by: Arnd Bergmann <arnd@arndb.de>
> Acked-by: Nicolas Pitre <nico@linaro.org>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> Hi Greg,
>
> As Ard pointed out, commit 13d1b9575ac2c2da ("ARM: 8221/1: PJ4: allow
> building in Thumb-2 mode") which I suggested for backports into
> 3.16 is broken unless we also take this one.
>
> I checked the other stable branches and found that both 3.18 and
> 4.4 contain only the first of the two, so please apply this one on
> both branches as well.

Clarification: please apply this patch from email on 3.18.y and
cherry-pick the original 5008efc83bf85b6 on 4.4.y to avoid
rebasing yourself.

        Arnd

Re: [PATCH] [stable 3.18 through 4.4] ARM: 8452/3: PJ4: make coprocessor access sequences buildable in Thumb2 mode

[gregkh]

On Mon, May 08, 2017 at 09:57:54PM +0200, Arnd Bergmann wrote:
> On Mon, May 8, 2017 at 9:55 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> > From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >
> > Commit 5008efc83bf85b647aa1cbc44718b1675bbb7444 upstream.
> >
> > The PJ4 inline asm sequence to write to cp15 cannot be built in Thumb-2
> > mode, due to the way it performs arithmetic on the program counter, so it
> > is built in ARM mode instead. However, building C files in ARM mode under
> > CONFIG_THUMB2_KERNEL is problematic, since the instrumentation performed
> > by subsystems like ftrace does not expect having to deal with interworking
> > branches.
> >
> > Since the sequence in question is simply a poor man's ISB instruction,
> > let's use a straight 'isb' instead when building in Thumb2 mode. Thumb2
> > implies V7, so 'isb' should always be supported in that case.
> >
> > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > Acked-by: Nicolas Pitre <nico@linaro.org>
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > Hi Greg,
> >
> > As Ard pointed out, commit 13d1b9575ac2c2da ("ARM: 8221/1: PJ4: allow
> > building in Thumb-2 mode") which I suggested for backports into
> > 3.16 is broken unless we also take this one.
> >
> > I checked the other stable branches and found that both 3.18 and
> > 4.4 contain only the first of the two, so please apply this one on
> > both branches as well.
> 
> Clarification: please apply this patch from email on 3.18.y and
> cherry-pick the original 5008efc83bf85b6 on 4.4.y to avoid
> rebasing yourself.

Now queued up this way, thanks.

greg k-h