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Date: Tue, 5 Jan 2010 17:37:08 -0800 (PST)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
cc: Minchan Kim <minchan.kim@...il.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Peter Zijlstra <peterz@...radead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>, cl@...ux-foundation.org,
"hugh.dickins" <hugh.dickins@...cali.co.uk>,
Nick Piggin <nickpiggin@...oo.com.au>,
Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()
On Wed, 6 Jan 2010, KAMEZAWA Hiroyuki wrote:
>
> I think this is the 1st reason but haven't rewrote rwsem itself and tested,
> sorry.
Here's a totally untested patch! It may or may not work. It builds for me,
but that may be some cosmic accident. I _think_ I got the callee-clobbered
register set right, but somebody should check the comment in the new
rwsem_64.S, and double-check that the code actually matches what I tried
to do.
I had to change the inline asm to get the register sizes right too, so for
all I know this screws up x86-32 too.
In other words: UNTESTED! It may molest your pets and drink all your beer.
You have been warned.
(Is a 16-bit rwsem count even enough for x86-64? Possibly not. That's a
separate issue entirely, though).
Linus
---
arch/x86/Kconfig.cpu | 2 +-
arch/x86/include/asm/rwsem.h | 18 +++++-----
arch/x86/lib/Makefile | 1 +
arch/x86/lib/rwsem_64.S | 81 ++++++++++++++++++++++++++++++++++++++++++
4 files changed, 92 insertions(+), 10 deletions(-)
diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index f20ddf8..a198293 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -319,7 +319,7 @@ config X86_L1_CACHE_SHIFT
config X86_XADD
def_bool y
- depends on X86_32 && !M386
+ depends on X86_64 || !M386
config X86_PPRO_FENCE
bool "PentiumPro memory ordering errata workaround"
diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h
index ca7517d..625baca 100644
--- a/arch/x86/include/asm/rwsem.h
+++ b/arch/x86/include/asm/rwsem.h
@@ -65,7 +65,7 @@ extern asmregparm struct rw_semaphore *
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
struct rw_semaphore {
- signed long count;
+ __s32 count;
spinlock_t wait_lock;
struct list_head wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -105,7 +105,7 @@ do { \
static inline void __down_read(struct rw_semaphore *sem)
{
asm volatile("# beginning down_read\n\t"
- LOCK_PREFIX " incl (%%eax)\n\t"
+ LOCK_PREFIX " incl (%1)\n\t"
/* adds 0x00000001, returns the old value */
" jns 1f\n"
" call call_rwsem_down_read_failed\n"
@@ -147,7 +147,7 @@ static inline void __down_write_nested(struct rw_semaphore *sem, int subclass)
tmp = RWSEM_ACTIVE_WRITE_BIAS;
asm volatile("# beginning down_write\n\t"
- LOCK_PREFIX " xadd %%edx,(%%eax)\n\t"
+ LOCK_PREFIX " xaddl %%edx,(%2)\n\t"
/* subtract 0x0000ffff, returns the old value */
" testl %%edx,%%edx\n\t"
/* was the count 0 before? */
@@ -170,9 +170,9 @@ static inline void __down_write(struct rw_semaphore *sem)
*/
static inline int __down_write_trylock(struct rw_semaphore *sem)
{
- signed long ret = cmpxchg(&sem->count,
- RWSEM_UNLOCKED_VALUE,
- RWSEM_ACTIVE_WRITE_BIAS);
+ __s32 ret = cmpxchg(&sem->count,
+ RWSEM_UNLOCKED_VALUE,
+ RWSEM_ACTIVE_WRITE_BIAS);
if (ret == RWSEM_UNLOCKED_VALUE)
return 1;
return 0;
@@ -185,7 +185,7 @@ static inline void __up_read(struct rw_semaphore *sem)
{
__s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
asm volatile("# beginning __up_read\n\t"
- LOCK_PREFIX " xadd %%edx,(%%eax)\n\t"
+ LOCK_PREFIX " xaddl %%edx,(%2)\n\t"
/* subtracts 1, returns the old value */
" jns 1f\n\t"
" call call_rwsem_wake\n"
@@ -203,7 +203,7 @@ static inline void __up_write(struct rw_semaphore *sem)
{
asm volatile("# beginning __up_write\n\t"
" movl %2,%%edx\n\t"
- LOCK_PREFIX " xaddl %%edx,(%%eax)\n\t"
+ LOCK_PREFIX " xaddl %%edx,(%1)\n\t"
/* tries to transition
0xffff0001 -> 0x00000000 */
" jz 1f\n"
@@ -221,7 +221,7 @@ static inline void __up_write(struct rw_semaphore *sem)
static inline void __downgrade_write(struct rw_semaphore *sem)
{
asm volatile("# beginning __downgrade_write\n\t"
- LOCK_PREFIX " addl %2,(%%eax)\n\t"
+ LOCK_PREFIX " addl %2,(%1)\n\t"
/* transitions 0xZZZZ0001 -> 0xYYYY0001 */
" jns 1f\n\t"
" call call_rwsem_downgrade_wake\n"
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index cffd754..c802451 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -39,4 +39,5 @@ else
lib-y += thunk_64.o clear_page_64.o copy_page_64.o
lib-y += memmove_64.o memset_64.o
lib-y += copy_user_64.o rwlock_64.o copy_user_nocache_64.o
+ lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem_64.o
endif
diff --git a/arch/x86/lib/rwsem_64.S b/arch/x86/lib/rwsem_64.S
new file mode 100644
index 0000000..15acecf
--- /dev/null
+++ b/arch/x86/lib/rwsem_64.S
@@ -0,0 +1,81 @@
+/*
+ * x86-64 rwsem wrappers
+ *
+ * This interfaces the inline asm code to the slow-path
+ * C routines. We need to save the call-clobbered regs
+ * that the asm does not mark as clobbered, and move the
+ * argument from %rax to %rdi.
+ *
+ * NOTE! We don't need to save %rax, because the functions
+ * will always return the semaphore pointer in %rax (which
+ * is also the input argument to these helpers)
+ *
+ * The following can clobber %rdx because the asm clobbers it:
+ * call_rwsem_down_write_failed
+ * call_rwsem_wake
+ * but %rdi, %rsi, %rcx, %r8-r11 always need saving.
+ */
+
+#include <linux/linkage.h>
+#include <asm/rwlock.h>
+#include <asm/alternative-asm.h>
+#include <asm/frame.h>
+#include <asm/dwarf2.h>
+
+#define save_common_regs \
+ pushq %rdi; \
+ pushq %rsi; \
+ pushq %rcx; \
+ pushq %r8; \
+ pushq %r9; \
+ pushq %r10; \
+ pushq %r11
+
+#define restore_common_regs \
+ popq %r11; \
+ popq %r10; \
+ popq %r9; \
+ popq %r8; \
+ popq %rcx; \
+ popq %rsi; \
+ popq %rdi
+
+/* Fix up special calling conventions */
+ENTRY(call_rwsem_down_read_failed)
+ save_common_regs
+ pushq %rdx
+ movq %rax,%rdi
+ call rwsem_down_read_failed
+ popq %rdx
+ restore_common_regs
+ ret
+ ENDPROC(call_rwsem_down_read_failed)
+
+ENTRY(call_rwsem_down_write_failed)
+ save_common_regs
+ movq %rax,%rdi
+ call rwsem_down_write_failed
+ restore_common_regs
+ ret
+ ENDPROC(call_rwsem_down_write_failed)
+
+ENTRY(call_rwsem_wake)
+ decw %dx /* do nothing if still outstanding active readers */
+ jnz 1f
+ save_common_regs
+ movq %rax,%rdi
+ call rwsem_wake
+ restore_common_regs
+1: ret
+ ENDPROC(call_rwsem_wake)
+
+/* Fix up special calling conventions */
+ENTRY(call_rwsem_downgrade_wake)
+ save_common_regs
+ pushq %rdx
+ movq %rax,%rdi
+ call rwsem_downgrade_wake
+ popq %rdx
+ restore_common_regs
+ ret
+ ENDPROC(call_rwsem_downgrade_wake)
--
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