[PATCH v2] powerpc: select ARCH_HAS_MEMBARRIER_SYNC_CORE

Nicholas Piggin
2020-07-15T09:48:39Z

powerpc return from interrupt and return from system call sequences are
context synchronising.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
v2: add more comments

.../features/sched/membarrier-sync-core/arch-support.txt | 4 ++--
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/exception-64e.h | 6 +++++-
arch/powerpc/include/asm/exception-64s.h | 7 +++++++
arch/powerpc/kernel/entry_32.S | 6 ++++++
5 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/Documentation/features/sched/membarrier-sync-core/arch-support.txt b/Documentation/features/sched/membarrier-sync-core/arch-support.txt
index 8a521a622966..52ad74a25f54 100644
--- a/Documentation/features/sched/membarrier-sync-core/arch-support.txt
+++ b/Documentation/features/sched/membarrier-sync-core/arch-support.txt
@@ -5,7 +5,7 @@
#
# Architecture requirements
#
-# * arm/arm64
+# * arm/arm64/powerpc
#
# Rely on implicit context synchronization as a result of exception return
# when returning from IPI handler, and when returning to user-space.
@@ -45,7 +45,7 @@
| nios2: | TODO |
| openrisc: | TODO |
| parisc: | TODO |
- | powerpc: | TODO |
+ | powerpc: | ok |
| riscv: | TODO |
| s390: | TODO |
| sh: | TODO |
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 9fa23eb320ff..920c4e3ca4ef 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -131,6 +131,7 @@ config PPC
select ARCH_HAS_PTE_DEVMAP if PPC_BOOK3S_64
select ARCH_HAS_PTE_SPECIAL
select ARCH_HAS_MEMBARRIER_CALLBACKS
+ select ARCH_HAS_MEMBARRIER_SYNC_CORE
select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
select ARCH_HAS_STRICT_KERNEL_RWX if (PPC32 && !HIBERNATION)
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
diff --git a/arch/powerpc/include/asm/exception-64e.h b/arch/powerpc/include/asm/exception-64e.h
index 54a98ef7d7fe..071d7ccb830f 100644
--- a/arch/powerpc/include/asm/exception-64e.h
+++ b/arch/powerpc/include/asm/exception-64e.h
@@ -204,7 +204,11 @@ exc_##label##_book3e:
LOAD_REG_ADDR(r3,interrupt_base_book3e);\
ori r3,r3,vector_offset@l; \
mtspr SPRN_IVOR##vector_number,r3;
-
+/*
+ * powerpc relies on return from interrupt/syscall being context synchronising
+ * (which rfi is) to support ARCH_HAS_MEMBARRIER_SYNC_CORE without additional
+ * additional synchronisation instructions.
+ */
#define RFI_TO_KERNEL \
rfi

diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h
index 47bd4ea0837d..a4704f405e8d 100644
--- a/arch/powerpc/include/asm/exception-64s.h
+++ b/arch/powerpc/include/asm/exception-64s.h
@@ -68,6 +68,13 @@
*
* The nop instructions allow us to insert one or more instructions to flush the
* L1-D cache when returning to userspace or a guest.
+ *
+ * powerpc relies on return from interrupt/syscall being context synchronising
+ * (which hrfid, rfid, and rfscv are) to support ARCH_HAS_MEMBARRIER_SYNC_CORE
+ * without additional additional synchronisation instructions. soft-masked
+ * interrupt replay does not include a context-synchronising rfid, but those
+ * always return to kernel, the context sync is only required for IPIs which
+ * return to user.
*/
#define RFI_FLUSH_SLOT \
RFI_FLUSH_FIXUP_SECTION; \
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 217ebdf5b00b..23bb7352e7c3 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -35,6 +35,12 @@

#include "head_32.h"

+/*
+ * powerpc relies on return from interrupt/syscall being context synchronising
+ * (which rfi is) to support ARCH_HAS_MEMBARRIER_SYNC_CORE without additional
+ * additional synchronisation instructions.
+ */
+
/*
* Align to 4k in order to ensure that all functions modyfing srr0/srr1
* fit into one page in order to not encounter a TLB miss between the
--
2.23.0