[PATCH for 4.9/4.14] powerpc: Fix incorrect stw{, ux, u, x} instructions in __set_pte_at

From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Backport for 4.9 and 4.14

(cherry picked from commit d85be8a49e733dcd23674aa6202870d54bf5600d)

The placeholder for instruction selection should use the second
argument's operand, which is %1, not %0. This could generate incorrect
assembly code if the memory addressing of operand %0 is a different
form from that of operand %1.

Also remove the %Un placeholder because having %Un placeholders
for two operands which are based on the same local var (ptep) doesn't
make much sense. By the way, it doesn't change the current behaviour
because "<>" constraint is missing for the associated "=m".

[chleroy: revised commit log iaw segher's comments and removed %U0]

Fixes: 9bf2b5cdc5fe ("powerpc: Fixes for CONFIG_PTE_64BIT for SMP support")
Cc: <redacted> # v2.6.28+
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Christophe Leroy <redacted>
Acked-by: Segher Boessenkool <redacted>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/96354bd77977a6a933fe9020da57629007fdb920.1603358942.git.christophe.leroy@csgroup.eu
---
 arch/powerpc/include/asm/book3s/32/pgtable.h | 4 ++--
 arch/powerpc/include/asm/nohash/pgtable.h    | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h b/arch/powerpc/include/asm/book3s/32/pgtable.h
index 016579ef16d3..ec98abca0df0 100644
--- a/arch/powerpc/include/asm/book3s/32/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/32/pgtable.h

@@ -414,9 +414,9 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
 	if (pte_val(*ptep) & _PAGE_HASHPTE)
 		flush_hash_entry(mm, ptep, addr);
 	__asm__ __volatile__("\
-		stw%U0%X0 %2,%0\n\
+		stw%X0 %2,%0\n\
 		eieio\n\
-		stw%U0%X0 %L2,%1"
+		stw%X1 %L2,%1"
 	: "=m" (*ptep), "=m" (*((unsigned char *)ptep+4))
 	: "r" (pte) : "memory");
 

diff --git a/arch/powerpc/include/asm/nohash/pgtable.h b/arch/powerpc/include/asm/nohash/pgtable.h
index 5c68f4a59f75..e9171b8242e4 100644
--- a/arch/powerpc/include/asm/nohash/pgtable.h
+++ b/arch/powerpc/include/asm/nohash/pgtable.h

@@ -157,9 +157,9 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
 		flush_hash_entry(mm, ptep, addr);
 #endif
 	__asm__ __volatile__("\
-		stw%U0%X0 %2,%0\n\
+		stw%X0 %2,%0\n\
 		eieio\n\
-		stw%U0%X0 %L2,%1"
+		stw%X1 %L2,%1"
 	: "=m" (*ptep), "=m" (*((unsigned char *)ptep+4))
 	: "r" (pte) : "memory");
 

-- 
2.25.0

On Wed, Jan 13, 2021 at 07:12:44AM +0000, Christophe Leroy wrote:

From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Backport for 4.9 and 4.14

(cherry picked from commit d85be8a49e733dcd23674aa6202870d54bf5600d)

The placeholder for instruction selection should use the second
argument's operand, which is %1, not %0. This could generate incorrect
assembly code if the memory addressing of operand %0 is a different
form from that of operand %1.

Also remove the %Un placeholder because having %Un placeholders
for two operands which are based on the same local var (ptep) doesn't
make much sense. By the way, it doesn't change the current behaviour
because "<>" constraint is missing for the associated "=m".

[chleroy: revised commit log iaw segher's comments and removed %U0]

Fixes: 9bf2b5cdc5fe ("powerpc: Fixes for CONFIG_PTE_64BIT for SMP support")
Cc: <redacted> # v2.6.28+
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Christophe Leroy <redacted>
Acked-by: Segher Boessenkool <redacted>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/96354bd77977a6a933fe9020da57629007fdb920.1603358942.git.christophe.leroy@csgroup.eu

I took this and the 4.4 backport, thanks!

-- 
Thanks,
Sasha