[PATCH v6 0/4] Align atomic storage

[PATCH v6 0/4] Align atomic storage

[Finn Thain]

This series adds the __aligned attribute to atomic_t and atomic64_t
definitions in include/linux and include/asm-generic (respectively)
to get natural alignment of both types on csky, m68k, microblaze,
nios2, openrisc and sh.

This series also adds Kconfig options to enable a new run-time warning
to help reveal misaligned atomic accesses on platforms which don't
trap that.

The performance impact is expected to vary across platforms and workloads.
The measurements I made on m68k show that some workloads run faster and
others slower.

---

Changed since v5:
 - Added acked-by and revewed-by tags.
 - Added a new macro to inhibit emission of __bug_table section, for the
 benefit of pre-boot code like the EFI stub loader.

Changed since v4:
 - Dropped parisc header file patch as it's been merged already.
 - Submitted as PATCH instead of RFC.

Changed since v3:
 - Rebased on v6.17.
 - New patch to resolve header dependency issue on parisc.
 - Dropped documentation patch.

Changed since v2:
 - Specify natural alignment for atomic64_t.
 - CONFIG_DEBUG_ATOMIC checks for natural alignment again.
 - New patch to add weakened alignment check.
 - New patch for explicit alignment in BPF header.

---

Finn Thain (3):
  bpf: Explicitly align bpf_res_spin_lock
  atomic: Specify alignment for atomic_t and atomic64_t
  atomic: Add option for weaker alignment check

Peter Zijlstra (1):
  atomic: Add alignment check to instrumented atomic operations

 arch/x86/boot/compressed/Makefile     |  1 +
 drivers/firmware/efi/libstub/Makefile |  1 +
 include/asm-generic/atomic64.h        |  2 +-
 include/asm-generic/rqspinlock.h      |  2 +-
 include/linux/instrumented.h          | 17 +++++++++++++++++
 include/linux/types.h                 |  2 +-
 kernel/bpf/rqspinlock.c               |  1 -
 lib/Kconfig.debug                     | 18 ++++++++++++++++++
 8 files changed, 40 insertions(+), 4 deletions(-)

-- 
2.49.1

[PATCH v6 2/4] atomic: Specify alignment for atomic_t and atomic64_t

[Finn Thain]

Some recent commits incorrectly assumed 4-byte alignment of locks.
That assumption fails on Linux/m68k (and, interestingly, would have
failed on Linux/cris also). The jump label implementation makes a
similar alignment assumption.

The expectation that atomic_t and atomic64_t variables will be naturally
aligned seems reasonable, as indeed they are on 64-bit architectures.
But atomic64_t isn't naturally aligned on csky, m68k, microblaze, nios2,
openrisc and sh. Neither atomic_t nor atomic64_t are naturally aligned
on m68k.

This patch brings a little uniformity by specifying natural alignment
for atomic types. One benefit is that atomic64_t variables do not get
split across a page boundary. The cost is that some structs grow which
leads to cache misses and wasted memory.

Cc: Guo Ren <guoren@kernel.org>
Cc: linux-csky@vger.kernel.org
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-m68k@lists.linux-m68k.org
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Cc: Stafford Horne <shorne@gmail.com>
Cc: linux-openrisc@vger.kernel.org
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Rich Felker <dalias@libc.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: linux-sh@vger.kernel.org
Link: https://lore.kernel.org/lkml/CAFr9PX=MYUDGJS2kAvPMkkfvH+0-SwQB_kxE4ea0J_wZ_pk=7w@mail.gmail.com
Link: https://lore.kernel.org/lkml/CAMuHMdW7Ab13DdGs2acMQcix5ObJK0O2dG_Fxzr8_g58Rc1_0g@mail.gmail.com/
Acked-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
---
Changed since v5:
 - Added tags from Guo Ren and Arnd Bergmann.

Changed since v2:
 - Specify natural alignment for atomic64_t.

Changed since v1:
 - atomic64_t now gets an __aligned attribute too.
 - The 'Fixes' tag has been dropped because Lance sent a different fix
   for commit e711faaafbe5 ("hung_task: replace blocker_mutex with encoded
   blocker") that's suitable for -stable.
---
 include/asm-generic/atomic64.h | 2 +-
 include/linux/types.h          | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/atomic64.h b/include/asm-generic/atomic64.h
index 100d24b02e52..f22ccfc0df98 100644
--- a/include/asm-generic/atomic64.h
+++ b/include/asm-generic/atomic64.h
@@ -10,7 +10,7 @@
 #include <linux/types.h>
 
 typedef struct {
-	s64 counter;
+	s64 __aligned(sizeof(s64)) counter;
 } atomic64_t;
 
 #define ATOMIC64_INIT(i)	{ (i) }
diff --git a/include/linux/types.h b/include/linux/types.h
index d4437e9c452c..1760e1feeab9 100644
--- a/include/linux/types.h
+++ b/include/linux/types.h
@@ -180,7 +180,7 @@ typedef phys_addr_t resource_size_t;
 typedef unsigned long irq_hw_number_t;
 
 typedef struct {
-	int counter;
+	int __aligned(sizeof(int)) counter;
 } atomic_t;
 
 #define ATOMIC_INIT(i) { (i) }
-- 
2.49.1