This series enables PREEMPT_DYNAMIC on arm64. To do so, it adds a new
mechanism allowing the preemption functions to be enabled/disabled using
static keys rather than static calls, with architectures selecting
whether they use static calls or static keys.
With non-inline static calls, each function call results in a call to
the (out-of-line) trampoline which either tail-calls its associated
callee or performs an early return.
The key idea is that where we're only enabling/disabling a single
callee, we can inline this trampoline into the start of the callee,
using a static key to decide whether to return early, and leaving the
remaining codegen to the compiler. The overhead should be similar to
(and likely lower than) using a static call trampoline. Since most
codegen is up to the compiler, we sidestep a number of implementation
pain-points (e.g. things like CFI should "just work" as well as they do
for any other functions).
The bulk of the diffstat for kernel/sched/core.c is shuffling the
PREEMPT_DYNAMIC code later in the file, and the actual additions are
fairly trivial.
I've given this very light build+boot testing so far.
Since v1 [1]:
* Rework Kconfig text to be clearer
* Rework arm64 entry code
* Clarify commit messages.
Since v2 [2]:
* Add missing includes
* Always provide prototype for preempt_schedule()
* Always provide prototype for preempt_schedule_notrace()
* Fix __cond_resched() to default to disabled
* Fix might_resched() to default to disabled
* Clarify example in commit message
Since v3 [3]:
* Add acks (including those missing from v3)
* Fix Kconfig dependencies for jump labels
* Don't default-enable PREEMPT_DYNAMIC when using static keys
* Clarify generated assembly examples
[1] https://lore.kernel.org/r/[email protected]/
[2] https://lore.kernel.org/r/[email protected]/
[3] https://lore.kernel.org/r/[email protected]/
Thanks,
Mark.
Mark Rutland (7):
sched/preempt: move PREEMPT_DYNAMIC logic later
sched/preempt: refactor sched_dynamic_update()
sched/preempt: simplify irqentry_exit_cond_resched() callers
sched/preempt: decouple HAVE_PREEMPT_DYNAMIC from GENERIC_ENTRY
sched/preempt: add PREEMPT_DYNAMIC using static keys
arm64: entry: centralize preemption decision
arm64: support PREEMPT_DYNAMIC
arch/Kconfig | 37 +++-
arch/arm64/Kconfig | 1 +
arch/arm64/include/asm/preempt.h | 19 +-
arch/arm64/kernel/entry-common.c | 28 ++-
arch/x86/Kconfig | 2 +-
arch/x86/include/asm/preempt.h | 10 +-
include/linux/entry-common.h | 15 +-
include/linux/kernel.h | 7 +-
include/linux/sched.h | 10 +-
kernel/Kconfig.preempt | 3 +-
kernel/entry/common.c | 23 +-
kernel/sched/core.c | 347 ++++++++++++++++++-------------
12 files changed, 329 insertions(+), 173 deletions(-)
--
2.30.2
Currently sched_dynamic_update needs to open-code the enabled/disabled
function names for each preemption model it supports, when in practice
this is a boolean enabled/disabled state for each function.
Make this clearer and avoid repetition by defining the enabled/disabled
states at the function definition, and using helper macros to perform the
static_call_update(). Where x86 currently overrides the enabled
function, it is made to provide both the enabled and disabled states for
consistency, with defaults provided by the core code otherwise.
In subsequent patches this will allow us to support PREEMPT_DYNAMIC
without static calls.
There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Valentin Schneider <[email protected]>
---
arch/x86/include/asm/preempt.h | 10 +++---
include/linux/entry-common.h | 2 ++
kernel/sched/core.c | 59 +++++++++++++++++++++-------------
3 files changed, 45 insertions(+), 26 deletions(-)
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index fe5efbcba824..5f6daea1ee24 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -108,16 +108,18 @@ static __always_inline bool should_resched(int preempt_offset)
extern asmlinkage void preempt_schedule(void);
extern asmlinkage void preempt_schedule_thunk(void);
-#define __preempt_schedule_func preempt_schedule_thunk
+#define preempt_schedule_dynamic_enabled preempt_schedule_thunk
+#define preempt_schedule_dynamic_disabled NULL
extern asmlinkage void preempt_schedule_notrace(void);
extern asmlinkage void preempt_schedule_notrace_thunk(void);
-#define __preempt_schedule_notrace_func preempt_schedule_notrace_thunk
+#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace_thunk
+#define preempt_schedule_notrace_dynamic_disabled NULL
#ifdef CONFIG_PREEMPT_DYNAMIC
-DECLARE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
+DECLARE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
#define __preempt_schedule() \
do { \
@@ -125,7 +127,7 @@ do { \
asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
} while (0)
-DECLARE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
+DECLARE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
#define __preempt_schedule_notrace() \
do { \
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 2e2b8d6140ed..a01ac1a0a292 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -456,6 +456,8 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
*/
void irqentry_exit_cond_resched(void);
#ifdef CONFIG_PREEMPT_DYNAMIC
+#define irqentry_exit_cond_resched_dynamic_enabled irqentry_exit_cond_resched
+#define irqentry_exit_cond_resched_dynamic_disabled NULL
DECLARE_STATIC_CALL(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6e8998267102..414165c430f4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6489,7 +6489,11 @@ NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);
#ifdef CONFIG_PREEMPT_DYNAMIC
-DEFINE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
+#ifndef preempt_schedule_dynamic_enabled
+#define preempt_schedule_dynamic_enabled preempt_schedule
+#define preempt_schedule_dynamic_disabled NULL
+#endif
+DEFINE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
#endif
@@ -6547,7 +6551,11 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
#ifdef CONFIG_PREEMPT_DYNAMIC
-DEFINE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
+#ifndef preempt_schedule_notrace_dynamic_enabled
+#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace
+#define preempt_schedule_notrace_dynamic_disabled NULL
+#endif
+DEFINE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
#endif
@@ -8058,9 +8066,13 @@ EXPORT_SYMBOL(__cond_resched);
#endif
#ifdef CONFIG_PREEMPT_DYNAMIC
+#define cond_resched_dynamic_enabled __cond_resched
+#define cond_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(cond_resched);
+#define might_resched_dynamic_enabled __cond_resched
+#define might_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(might_resched);
#endif
@@ -8184,43 +8196,46 @@ int sched_dynamic_mode(const char *str)
return -EINVAL;
}
+#define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled)
+#define preempt_dynamic_disable(f) static_call_update(f, f##_dynamic_disabled)
+
void sched_dynamic_update(int mode)
{
/*
* Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
* the ZERO state, which is invalid.
*/
- static_call_update(cond_resched, __cond_resched);
- static_call_update(might_resched, __cond_resched);
- static_call_update(preempt_schedule, __preempt_schedule_func);
- static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
- static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+ preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(might_resched);
+ preempt_dynamic_enable(preempt_schedule);
+ preempt_dynamic_enable(preempt_schedule_notrace);
+ preempt_dynamic_enable(irqentry_exit_cond_resched);
switch (mode) {
case preempt_dynamic_none:
- static_call_update(cond_resched, __cond_resched);
- static_call_update(might_resched, (void *)&__static_call_return0);
- static_call_update(preempt_schedule, NULL);
- static_call_update(preempt_schedule_notrace, NULL);
- static_call_update(irqentry_exit_cond_resched, NULL);
+ preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_disable(might_resched);
+ preempt_dynamic_disable(preempt_schedule);
+ preempt_dynamic_disable(preempt_schedule_notrace);
+ preempt_dynamic_disable(irqentry_exit_cond_resched);
pr_info("Dynamic Preempt: none\n");
break;
case preempt_dynamic_voluntary:
- static_call_update(cond_resched, __cond_resched);
- static_call_update(might_resched, __cond_resched);
- static_call_update(preempt_schedule, NULL);
- static_call_update(preempt_schedule_notrace, NULL);
- static_call_update(irqentry_exit_cond_resched, NULL);
+ preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(might_resched);
+ preempt_dynamic_disable(preempt_schedule);
+ preempt_dynamic_disable(preempt_schedule_notrace);
+ preempt_dynamic_disable(irqentry_exit_cond_resched);
pr_info("Dynamic Preempt: voluntary\n");
break;
case preempt_dynamic_full:
- static_call_update(cond_resched, (void *)&__static_call_return0);
- static_call_update(might_resched, (void *)&__static_call_return0);
- static_call_update(preempt_schedule, __preempt_schedule_func);
- static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
- static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+ preempt_dynamic_disable(cond_resched);
+ preempt_dynamic_disable(might_resched);
+ preempt_dynamic_enable(preempt_schedule);
+ preempt_dynamic_enable(preempt_schedule_notrace);
+ preempt_dynamic_enable(irqentry_exit_cond_resched);
pr_info("Dynamic Preempt: full\n");
break;
}
--
2.30.2
Where an architecture selects HAVE_STATIC_CALL but not
HAVE_STATIC_CALL_INLINE, each static call has an out-of-line trampoline
which will either branch to a callee or return to the caller.
On such architectures, a number of constraints can conspire to make
those trampolines more complicated and potentially less useful than we'd
like. For example:
* Hardware and software control flow integrity schemes can require the
addition of "landing pad" instructions (e.g. `BTI` for arm64), which
will also be present at the "real" callee.
* Limited branch ranges can require that trampolines generate or load an
address into a register and perform an indirect branch (or at least
have a slow path that does so). This loses some of the benefits of
having a direct branch.
* Interaction with SW CFI schemes can be complicated and fragile, e.g.
requiring that we can recognise idiomatic codegen and remove
indirections understand, at least until clang proves more helpful
mechanisms for dealing with this.
For PREEMPT_DYNAMIC, we don't need the full power of static calls, as we
really only need to enable/disable specific preemption functions. We can
achieve the same effect without a number of the pain points above by
using static keys to fold early returns into the preemption functions
themselves rather than in an out-of-line trampoline, effectively
inlining the trampoline into the start of the function.
For arm64, this results in good code generation. For example, the
dynamic_cond_resched() wrapper looks as follows when enabled. When
disabled, the first `B` is replaced with a `NOP`, resulting in an early
return.
| <dynamic_cond_resched>:
| bti c
| b <dynamic_cond_resched+0x10> // or `nop`
| mov w0, #0x0
| ret
| mrs x0, sp_el0
| ldr x0, [x0, #8]
| cbnz x0, <dynamic_cond_resched+0x8>
| paciasp
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl <preempt_schedule_common>
| mov w0, #0x1
| ldp x29, x30, [sp], #16
| autiasp
| ret
... compared to the regular form of the function:
| <__cond_resched>:
| bti c
| mrs x0, sp_el0
| ldr x1, [x0, #8]
| cbz x1, <__cond_resched+0x18>
| mov w0, #0x0
| ret
| paciasp
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl <preempt_schedule_common>
| mov w0, #0x1
| ldp x29, x30, [sp], #16
| autiasp
| ret
Any architecture which implements static keys should be able to use this
to implement PREEMPT_DYNAMIC with similar cost to non-inlined static
calls. Since this is likely to have greater overhead than (inlined)
static calls, PREEMPT_DYNAMIC is only defaulted to enabled when
HAVE_PREEMPT_DYNAMIC_CALL is selected.
Signed-off-by: Mark Rutland <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Valentin Schneider <[email protected]>
---
arch/Kconfig | 36 ++++++++++++++++++++++--
arch/x86/Kconfig | 2 +-
include/linux/entry-common.h | 10 +++++--
include/linux/kernel.h | 7 ++++-
include/linux/sched.h | 10 ++++++-
kernel/Kconfig.preempt | 3 +-
kernel/entry/common.c | 11 ++++++++
kernel/sched/core.c | 54 ++++++++++++++++++++++++++++++++++--
8 files changed, 122 insertions(+), 11 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 601691f1570f..d544abd14c01 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1278,11 +1278,41 @@ config HAVE_STATIC_CALL_INLINE
config HAVE_PREEMPT_DYNAMIC
bool
+
+config HAVE_PREEMPT_DYNAMIC_CALL
+ bool
depends on HAVE_STATIC_CALL
+ select HAVE_PREEMPT_DYNAMIC
+ help
+ An architecture should select this if it can handle the preemption
+ model being selected at boot time using static calls.
+
+ Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
+ preemption function will be patched directly.
+
+ Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
+ call to a preemption function will go through a trampoline, and the
+ trampoline will be patched.
+
+ It is strongly advised to support inline static call to avoid any
+ overhead.
+
+config HAVE_PREEMPT_DYNAMIC_KEY
+ bool
+ depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO
+ select HAVE_PREEMPT_DYNAMIC
help
- Select this if the architecture support boot time preempt setting
- on top of static calls. It is strongly advised to support inline
- static call to avoid any overhead.
+ An architecture should select this if it can handle the preemption
+ model being selected at boot time using static keys.
+
+ Each preemption function will be given an early return based on a
+ static key. This should have slightly lower overhead than non-inline
+ static calls, as this effectively inlines each trampoline into the
+ start of its callee. This may avoid redundant work, and may
+ integrate better with CFI schemes.
+
+ This will have greater overhead than using inline static calls as
+ the call to the preemption function cannot be entirely elided.
config ARCH_WANT_LD_ORPHAN_WARN
bool
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9f5bd41bf660..70f94094fd6f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -246,7 +246,7 @@ config X86
select HAVE_STACK_VALIDATION if X86_64
select HAVE_STATIC_CALL
select HAVE_STATIC_CALL_INLINE if HAVE_STACK_VALIDATION
- select HAVE_PREEMPT_DYNAMIC
+ select HAVE_PREEMPT_DYNAMIC_CALL
select HAVE_RSEQ
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_UNSTABLE_SCHED_CLOCK
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index dfd84c59b144..141952f4fee8 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -456,13 +456,19 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
*/
void raw_irqentry_exit_cond_resched(void);
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define irqentry_exit_cond_resched_dynamic_enabled raw_irqentry_exit_cond_resched
#define irqentry_exit_cond_resched_dynamic_disabled NULL
DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
#define irqentry_exit_cond_resched() static_call(irqentry_exit_cond_resched)()
-#else
-#define irqentry_exit_cond_resched() raw_irqentry_exit_cond_resched()
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
+void dynamic_irqentry_exit_cond_resched(void);
+#define irqentry_exit_cond_resched() dynamic_irqentry_exit_cond_resched()
#endif
+#else /* CONFIG_PREEMPT_DYNAMIC */
+#define irqentry_exit_cond_resched() raw_irqentry_exit_cond_resched()
+#endif /* CONFIG_PREEMPT_DYNAMIC */
/**
* irqentry_exit - Handle return from exception that used irqentry_enter()
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 33f47a996513..a890428bcc1a 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -99,7 +99,7 @@ struct user;
extern int __cond_resched(void);
# define might_resched() __cond_resched()
-#elif defined(CONFIG_PREEMPT_DYNAMIC)
+#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
extern int __cond_resched(void);
@@ -110,6 +110,11 @@ static __always_inline void might_resched(void)
static_call_mod(might_resched)();
}
+#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+
+extern int dynamic_might_resched(void);
+# define might_resched() dynamic_might_resched()
+
#else
# define might_resched() do { } while (0)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f5b2be39a78c..8b320fb54290 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2016,7 +2016,7 @@ static inline int test_tsk_need_resched(struct task_struct *tsk)
#if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
extern int __cond_resched(void);
-#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
DECLARE_STATIC_CALL(cond_resched, __cond_resched);
@@ -2025,6 +2025,14 @@ static __always_inline int _cond_resched(void)
return static_call_mod(cond_resched)();
}
+#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+extern int dynamic_cond_resched(void);
+
+static __always_inline int _cond_resched(void)
+{
+ return dynamic_cond_resched();
+}
+
#else
static inline int _cond_resched(void)
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index ce77f0265660..c2f1fd95a821 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -96,8 +96,9 @@ config PREEMPTION
config PREEMPT_DYNAMIC
bool "Preemption behaviour defined on boot"
depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
+ select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY
select PREEMPT_BUILD
- default y
+ default y if HAVE_PREEMPT_DYNAMIC_CALL
help
This option allows to define the preemption model on the kernel
command line parameter and thus override the default preemption
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 1739ca79613b..b145249ad91a 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -3,6 +3,7 @@
#include <linux/context_tracking.h>
#include <linux/entry-common.h>
#include <linux/highmem.h>
+#include <linux/jump_label.h>
#include <linux/livepatch.h>
#include <linux/audit.h>
#include <linux/tick.h>
@@ -392,7 +393,17 @@ void raw_irqentry_exit_cond_resched(void)
}
}
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
+void dynamic_irqentry_exit_cond_resched(void)
+{
+ if (!static_key_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
+ return;
+ raw_irqentry_exit_cond_resched();
+}
+#endif
#endif
noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3bf7f90d0ef7..4cca19d40636 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -14,6 +14,7 @@
#include <linux/nospec.h>
#include <linux/blkdev.h>
+#include <linux/jump_label.h>
#include <linux/kcov.h>
#include <linux/scs.h>
@@ -6482,21 +6483,31 @@ asmlinkage __visible void __sched notrace preempt_schedule(void)
*/
if (likely(!preemptible()))
return;
-
preempt_schedule_common();
}
NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#ifndef preempt_schedule_dynamic_enabled
#define preempt_schedule_dynamic_enabled preempt_schedule
#define preempt_schedule_dynamic_disabled NULL
#endif
DEFINE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule);
+void __sched notrace dynamic_preempt_schedule(void)
+{
+ if (!static_branch_unlikely(&sk_dynamic_preempt_schedule))
+ return;
+ preempt_schedule();
+}
+NOKPROBE_SYMBOL(dynamic_preempt_schedule);
+EXPORT_SYMBOL(dynamic_preempt_schedule);
+#endif
#endif
-
/**
* preempt_schedule_notrace - preempt_schedule called by tracing
@@ -6551,12 +6562,24 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#ifndef preempt_schedule_notrace_dynamic_enabled
#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace
#define preempt_schedule_notrace_dynamic_disabled NULL
#endif
DEFINE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule_notrace);
+void __sched notrace dynamic_preempt_schedule_notrace(void)
+{
+ if (!static_branch_unlikely(&sk_dynamic_preempt_schedule_notrace))
+ return;
+ preempt_schedule_notrace();
+}
+NOKPROBE_SYMBOL(dynamic_preempt_schedule_notrace);
+EXPORT_SYMBOL(dynamic_preempt_schedule_notrace);
+#endif
#endif
#endif /* CONFIG_PREEMPTION */
@@ -8066,6 +8089,7 @@ EXPORT_SYMBOL(__cond_resched);
#endif
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define cond_resched_dynamic_enabled __cond_resched
#define cond_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
@@ -8075,6 +8099,25 @@ EXPORT_STATIC_CALL_TRAMP(cond_resched);
#define might_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(might_resched);
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
+int __sched dynamic_cond_resched(void)
+{
+ if (!static_branch_unlikely(&sk_dynamic_cond_resched))
+ return 0;
+ return __cond_resched();
+}
+EXPORT_SYMBOL(dynamic_cond_resched);
+
+static DEFINE_STATIC_KEY_FALSE(sk_dynamic_might_resched);
+int __sched dynamic_might_resched(void)
+{
+ if (!static_branch_unlikely(&sk_dynamic_might_resched))
+ return 0;
+ return __cond_resched();
+}
+EXPORT_SYMBOL(dynamic_might_resched);
+#endif
#endif
/*
@@ -8198,8 +8241,15 @@ int sched_dynamic_mode(const char *str)
return -EINVAL;
}
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled)
#define preempt_dynamic_disable(f) static_call_update(f, f##_dynamic_disabled)
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+#define preempt_dynamic_enable(f) static_key_enable(&sk_dynamic_##f.key)
+#define preempt_dynamic_disable(f) static_key_disable(&sk_dynamic_##f.key)
+#else
+#error "Unsupported PREEMPT_DYNAMIC mechanism"
+#endif
void sched_dynamic_update(int mode)
{
--
2.30.2
On Mon, Feb 14, 2022 at 04:52:09PM +0000, Mark Rutland wrote:
> This series enables PREEMPT_DYNAMIC on arm64. To do so, it adds a new
> mechanism allowing the preemption functions to be enabled/disabled using
> static keys rather than static calls, with architectures selecting
> whether they use static calls or static keys.
>
> With non-inline static calls, each function call results in a call to
> the (out-of-line) trampoline which either tail-calls its associated
> callee or performs an early return.
>
> The key idea is that where we're only enabling/disabling a single
> callee, we can inline this trampoline into the start of the callee,
> using a static key to decide whether to return early, and leaving the
> remaining codegen to the compiler. The overhead should be similar to
> (and likely lower than) using a static call trampoline. Since most
> codegen is up to the compiler, we sidestep a number of implementation
> pain-points (e.g. things like CFI should "just work" as well as they do
> for any other functions).
>
> The bulk of the diffstat for kernel/sched/core.c is shuffling the
> PREEMPT_DYNAMIC code later in the file, and the actual additions are
> fairly trivial.
>
> I've given this very light build+boot testing so far.
Acked-by: Frederic Weisbecker <[email protected]>
Thanks!
On Thu, Feb 17, 2022 at 02:52:11PM +0100, Frederic Weisbecker wrote:
> On Mon, Feb 14, 2022 at 04:52:09PM +0000, Mark Rutland wrote:
> > This series enables PREEMPT_DYNAMIC on arm64. To do so, it adds a new
> > mechanism allowing the preemption functions to be enabled/disabled using
> > static keys rather than static calls, with architectures selecting
> > whether they use static calls or static keys.
> >
> > With non-inline static calls, each function call results in a call to
> > the (out-of-line) trampoline which either tail-calls its associated
> > callee or performs an early return.
> >
> > The key idea is that where we're only enabling/disabling a single
> > callee, we can inline this trampoline into the start of the callee,
> > using a static key to decide whether to return early, and leaving the
> > remaining codegen to the compiler. The overhead should be similar to
> > (and likely lower than) using a static call trampoline. Since most
> > codegen is up to the compiler, we sidestep a number of implementation
> > pain-points (e.g. things like CFI should "just work" as well as they do
> > for any other functions).
> >
> > The bulk of the diffstat for kernel/sched/core.c is shuffling the
> > PREEMPT_DYNAMIC code later in the file, and the actual additions are
> > fairly trivial.
> >
> > I've given this very light build+boot testing so far.
>
> Acked-by: Frederic Weisbecker <[email protected]>
I'll go stick them in sched/core then... :-)
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 8a69fe0be143b0a1af829f85f0e9a1ae7d6a04db
Gitweb: https://git.kernel.org/tip/8a69fe0be143b0a1af829f85f0e9a1ae7d6a04db
Author: Mark Rutland <[email protected]>
AuthorDate: Mon, 14 Feb 2022 16:52:11
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Sat, 19 Feb 2022 11:11:07 +01:00
sched/preempt: Refactor sched_dynamic_update()
Currently sched_dynamic_update needs to open-code the enabled/disabled
function names for each preemption model it supports, when in practice
this is a boolean enabled/disabled state for each function.
Make this clearer and avoid repetition by defining the enabled/disabled
states at the function definition, and using helper macros to perform the
static_call_update(). Where x86 currently overrides the enabled
function, it is made to provide both the enabled and disabled states for
consistency, with defaults provided by the core code otherwise.
In subsequent patches this will allow us to support PREEMPT_DYNAMIC
without static calls.
There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Acked-by: Frederic Weisbecker <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/include/asm/preempt.h | 10 +++---
include/linux/entry-common.h | 2 +-
kernel/sched/core.c | 59 ++++++++++++++++++++-------------
3 files changed, 45 insertions(+), 26 deletions(-)
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index fe5efbc..5f6daea 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -108,16 +108,18 @@ static __always_inline bool should_resched(int preempt_offset)
extern asmlinkage void preempt_schedule(void);
extern asmlinkage void preempt_schedule_thunk(void);
-#define __preempt_schedule_func preempt_schedule_thunk
+#define preempt_schedule_dynamic_enabled preempt_schedule_thunk
+#define preempt_schedule_dynamic_disabled NULL
extern asmlinkage void preempt_schedule_notrace(void);
extern asmlinkage void preempt_schedule_notrace_thunk(void);
-#define __preempt_schedule_notrace_func preempt_schedule_notrace_thunk
+#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace_thunk
+#define preempt_schedule_notrace_dynamic_disabled NULL
#ifdef CONFIG_PREEMPT_DYNAMIC
-DECLARE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
+DECLARE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
#define __preempt_schedule() \
do { \
@@ -125,7 +127,7 @@ do { \
asm volatile ("call " STATIC_CALL_TRAMP_STR(preempt_schedule) : ASM_CALL_CONSTRAINT); \
} while (0)
-DECLARE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
+DECLARE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
#define __preempt_schedule_notrace() \
do { \
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 2e2b8d6..a01ac1a 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -456,6 +456,8 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
*/
void irqentry_exit_cond_resched(void);
#ifdef CONFIG_PREEMPT_DYNAMIC
+#define irqentry_exit_cond_resched_dynamic_enabled irqentry_exit_cond_resched
+#define irqentry_exit_cond_resched_dynamic_disabled NULL
DECLARE_STATIC_CALL(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a123ffa..bf3a97f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6491,7 +6491,11 @@ NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);
#ifdef CONFIG_PREEMPT_DYNAMIC
-DEFINE_STATIC_CALL(preempt_schedule, __preempt_schedule_func);
+#ifndef preempt_schedule_dynamic_enabled
+#define preempt_schedule_dynamic_enabled preempt_schedule
+#define preempt_schedule_dynamic_disabled NULL
+#endif
+DEFINE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
#endif
@@ -6549,7 +6553,11 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
#ifdef CONFIG_PREEMPT_DYNAMIC
-DEFINE_STATIC_CALL(preempt_schedule_notrace, __preempt_schedule_notrace_func);
+#ifndef preempt_schedule_notrace_dynamic_enabled
+#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace
+#define preempt_schedule_notrace_dynamic_disabled NULL
+#endif
+DEFINE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
#endif
@@ -8060,9 +8068,13 @@ EXPORT_SYMBOL(__cond_resched);
#endif
#ifdef CONFIG_PREEMPT_DYNAMIC
+#define cond_resched_dynamic_enabled __cond_resched
+#define cond_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(cond_resched);
+#define might_resched_dynamic_enabled __cond_resched
+#define might_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(might_resched);
#endif
@@ -8192,43 +8204,46 @@ int sched_dynamic_mode(const char *str)
return -EINVAL;
}
+#define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled)
+#define preempt_dynamic_disable(f) static_call_update(f, f##_dynamic_disabled)
+
void sched_dynamic_update(int mode)
{
/*
* Avoid {NONE,VOLUNTARY} -> FULL transitions from ever ending up in
* the ZERO state, which is invalid.
*/
- static_call_update(cond_resched, __cond_resched);
- static_call_update(might_resched, __cond_resched);
- static_call_update(preempt_schedule, __preempt_schedule_func);
- static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
- static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+ preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(might_resched);
+ preempt_dynamic_enable(preempt_schedule);
+ preempt_dynamic_enable(preempt_schedule_notrace);
+ preempt_dynamic_enable(irqentry_exit_cond_resched);
switch (mode) {
case preempt_dynamic_none:
- static_call_update(cond_resched, __cond_resched);
- static_call_update(might_resched, (void *)&__static_call_return0);
- static_call_update(preempt_schedule, NULL);
- static_call_update(preempt_schedule_notrace, NULL);
- static_call_update(irqentry_exit_cond_resched, NULL);
+ preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_disable(might_resched);
+ preempt_dynamic_disable(preempt_schedule);
+ preempt_dynamic_disable(preempt_schedule_notrace);
+ preempt_dynamic_disable(irqentry_exit_cond_resched);
pr_info("Dynamic Preempt: none\n");
break;
case preempt_dynamic_voluntary:
- static_call_update(cond_resched, __cond_resched);
- static_call_update(might_resched, __cond_resched);
- static_call_update(preempt_schedule, NULL);
- static_call_update(preempt_schedule_notrace, NULL);
- static_call_update(irqentry_exit_cond_resched, NULL);
+ preempt_dynamic_enable(cond_resched);
+ preempt_dynamic_enable(might_resched);
+ preempt_dynamic_disable(preempt_schedule);
+ preempt_dynamic_disable(preempt_schedule_notrace);
+ preempt_dynamic_disable(irqentry_exit_cond_resched);
pr_info("Dynamic Preempt: voluntary\n");
break;
case preempt_dynamic_full:
- static_call_update(cond_resched, (void *)&__static_call_return0);
- static_call_update(might_resched, (void *)&__static_call_return0);
- static_call_update(preempt_schedule, __preempt_schedule_func);
- static_call_update(preempt_schedule_notrace, __preempt_schedule_notrace_func);
- static_call_update(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+ preempt_dynamic_disable(cond_resched);
+ preempt_dynamic_disable(might_resched);
+ preempt_dynamic_enable(preempt_schedule);
+ preempt_dynamic_enable(preempt_schedule_notrace);
+ preempt_dynamic_enable(irqentry_exit_cond_resched);
pr_info("Dynamic Preempt: full\n");
break;
}
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 99cf983cc8bca4adb461b519664c939a565cfd4d
Gitweb: https://git.kernel.org/tip/99cf983cc8bca4adb461b519664c939a565cfd4d
Author: Mark Rutland <[email protected]>
AuthorDate: Mon, 14 Feb 2022 16:52:14
Committer: Peter Zijlstra <[email protected]>
CommitterDate: Sat, 19 Feb 2022 11:11:08 +01:00
sched/preempt: Add PREEMPT_DYNAMIC using static keys
Where an architecture selects HAVE_STATIC_CALL but not
HAVE_STATIC_CALL_INLINE, each static call has an out-of-line trampoline
which will either branch to a callee or return to the caller.
On such architectures, a number of constraints can conspire to make
those trampolines more complicated and potentially less useful than we'd
like. For example:
* Hardware and software control flow integrity schemes can require the
addition of "landing pad" instructions (e.g. `BTI` for arm64), which
will also be present at the "real" callee.
* Limited branch ranges can require that trampolines generate or load an
address into a register and perform an indirect branch (or at least
have a slow path that does so). This loses some of the benefits of
having a direct branch.
* Interaction with SW CFI schemes can be complicated and fragile, e.g.
requiring that we can recognise idiomatic codegen and remove
indirections understand, at least until clang proves more helpful
mechanisms for dealing with this.
For PREEMPT_DYNAMIC, we don't need the full power of static calls, as we
really only need to enable/disable specific preemption functions. We can
achieve the same effect without a number of the pain points above by
using static keys to fold early returns into the preemption functions
themselves rather than in an out-of-line trampoline, effectively
inlining the trampoline into the start of the function.
For arm64, this results in good code generation. For example, the
dynamic_cond_resched() wrapper looks as follows when enabled. When
disabled, the first `B` is replaced with a `NOP`, resulting in an early
return.
| <dynamic_cond_resched>:
| bti c
| b <dynamic_cond_resched+0x10> // or `nop`
| mov w0, #0x0
| ret
| mrs x0, sp_el0
| ldr x0, [x0, #8]
| cbnz x0, <dynamic_cond_resched+0x8>
| paciasp
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl <preempt_schedule_common>
| mov w0, #0x1
| ldp x29, x30, [sp], #16
| autiasp
| ret
... compared to the regular form of the function:
| <__cond_resched>:
| bti c
| mrs x0, sp_el0
| ldr x1, [x0, #8]
| cbz x1, <__cond_resched+0x18>
| mov w0, #0x0
| ret
| paciasp
| stp x29, x30, [sp, #-16]!
| mov x29, sp
| bl <preempt_schedule_common>
| mov w0, #0x1
| ldp x29, x30, [sp], #16
| autiasp
| ret
Any architecture which implements static keys should be able to use this
to implement PREEMPT_DYNAMIC with similar cost to non-inlined static
calls. Since this is likely to have greater overhead than (inlined)
static calls, PREEMPT_DYNAMIC is only defaulted to enabled when
HAVE_PREEMPT_DYNAMIC_CALL is selected.
Signed-off-by: Mark Rutland <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
Acked-by: Frederic Weisbecker <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/Kconfig | 36 +++++++++++++++++++++--
arch/x86/Kconfig | 2 +-
include/linux/entry-common.h | 10 ++++--
include/linux/kernel.h | 7 ++++-
include/linux/sched.h | 10 +++++-
kernel/Kconfig.preempt | 3 +-
kernel/entry/common.c | 11 +++++++-
kernel/sched/core.c | 54 +++++++++++++++++++++++++++++++++--
8 files changed, 122 insertions(+), 11 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index 601691f..d544abd 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1278,11 +1278,41 @@ config HAVE_STATIC_CALL_INLINE
config HAVE_PREEMPT_DYNAMIC
bool
+
+config HAVE_PREEMPT_DYNAMIC_CALL
+ bool
depends on HAVE_STATIC_CALL
+ select HAVE_PREEMPT_DYNAMIC
+ help
+ An architecture should select this if it can handle the preemption
+ model being selected at boot time using static calls.
+
+ Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
+ preemption function will be patched directly.
+
+ Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
+ call to a preemption function will go through a trampoline, and the
+ trampoline will be patched.
+
+ It is strongly advised to support inline static call to avoid any
+ overhead.
+
+config HAVE_PREEMPT_DYNAMIC_KEY
+ bool
+ depends on HAVE_ARCH_JUMP_LABEL && CC_HAS_ASM_GOTO
+ select HAVE_PREEMPT_DYNAMIC
help
- Select this if the architecture support boot time preempt setting
- on top of static calls. It is strongly advised to support inline
- static call to avoid any overhead.
+ An architecture should select this if it can handle the preemption
+ model being selected at boot time using static keys.
+
+ Each preemption function will be given an early return based on a
+ static key. This should have slightly lower overhead than non-inline
+ static calls, as this effectively inlines each trampoline into the
+ start of its callee. This may avoid redundant work, and may
+ integrate better with CFI schemes.
+
+ This will have greater overhead than using inline static calls as
+ the call to the preemption function cannot be entirely elided.
config ARCH_WANT_LD_ORPHAN_WARN
bool
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ebe8fc7..f13cfdf 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -245,7 +245,7 @@ config X86
select HAVE_STACK_VALIDATION if X86_64
select HAVE_STATIC_CALL
select HAVE_STATIC_CALL_INLINE if HAVE_STACK_VALIDATION
- select HAVE_PREEMPT_DYNAMIC
+ select HAVE_PREEMPT_DYNAMIC_CALL
select HAVE_RSEQ
select HAVE_SYSCALL_TRACEPOINTS
select HAVE_UNSTABLE_SCHED_CLOCK
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index dfd84c5..141952f 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -456,13 +456,19 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
*/
void raw_irqentry_exit_cond_resched(void);
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define irqentry_exit_cond_resched_dynamic_enabled raw_irqentry_exit_cond_resched
#define irqentry_exit_cond_resched_dynamic_disabled NULL
DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
#define irqentry_exit_cond_resched() static_call(irqentry_exit_cond_resched)()
-#else
-#define irqentry_exit_cond_resched() raw_irqentry_exit_cond_resched()
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
+void dynamic_irqentry_exit_cond_resched(void);
+#define irqentry_exit_cond_resched() dynamic_irqentry_exit_cond_resched()
#endif
+#else /* CONFIG_PREEMPT_DYNAMIC */
+#define irqentry_exit_cond_resched() raw_irqentry_exit_cond_resched()
+#endif /* CONFIG_PREEMPT_DYNAMIC */
/**
* irqentry_exit - Handle return from exception that used irqentry_enter()
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 33f47a9..a890428 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -99,7 +99,7 @@ struct user;
extern int __cond_resched(void);
# define might_resched() __cond_resched()
-#elif defined(CONFIG_PREEMPT_DYNAMIC)
+#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
extern int __cond_resched(void);
@@ -110,6 +110,11 @@ static __always_inline void might_resched(void)
static_call_mod(might_resched)();
}
+#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+
+extern int dynamic_might_resched(void);
+# define might_resched() dynamic_might_resched()
+
#else
# define might_resched() do { } while (0)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 508b91d..de03dde 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2020,7 +2020,7 @@ static inline int test_tsk_need_resched(struct task_struct *tsk)
#if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC)
extern int __cond_resched(void);
-#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
DECLARE_STATIC_CALL(cond_resched, __cond_resched);
@@ -2029,6 +2029,14 @@ static __always_inline int _cond_resched(void)
return static_call_mod(cond_resched)();
}
+#elif defined(CONFIG_PREEMPT_DYNAMIC) && defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+extern int dynamic_cond_resched(void);
+
+static __always_inline int _cond_resched(void)
+{
+ return dynamic_cond_resched();
+}
+
#else
static inline int _cond_resched(void)
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index ce77f02..c2f1fd9 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -96,8 +96,9 @@ config PREEMPTION
config PREEMPT_DYNAMIC
bool "Preemption behaviour defined on boot"
depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
+ select JUMP_LABEL if HAVE_PREEMPT_DYNAMIC_KEY
select PREEMPT_BUILD
- default y
+ default y if HAVE_PREEMPT_DYNAMIC_CALL
help
This option allows to define the preemption model on the kernel
command line parameter and thus override the default preemption
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 1739ca7..b145249 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -3,6 +3,7 @@
#include <linux/context_tracking.h>
#include <linux/entry-common.h>
#include <linux/highmem.h>
+#include <linux/jump_label.h>
#include <linux/livepatch.h>
#include <linux/audit.h>
#include <linux/tick.h>
@@ -392,7 +393,17 @@ void raw_irqentry_exit_cond_resched(void)
}
}
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
+void dynamic_irqentry_exit_cond_resched(void)
+{
+ if (!static_key_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
+ return;
+ raw_irqentry_exit_cond_resched();
+}
+#endif
#endif
noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 300c045..9e65028 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -14,6 +14,7 @@
#include <linux/nospec.h>
#include <linux/blkdev.h>
+#include <linux/jump_label.h>
#include <linux/kcov.h>
#include <linux/scs.h>
@@ -6484,21 +6485,31 @@ asmlinkage __visible void __sched notrace preempt_schedule(void)
*/
if (likely(!preemptible()))
return;
-
preempt_schedule_common();
}
NOKPROBE_SYMBOL(preempt_schedule);
EXPORT_SYMBOL(preempt_schedule);
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#ifndef preempt_schedule_dynamic_enabled
#define preempt_schedule_dynamic_enabled preempt_schedule
#define preempt_schedule_dynamic_disabled NULL
#endif
DEFINE_STATIC_CALL(preempt_schedule, preempt_schedule_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule);
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule);
+void __sched notrace dynamic_preempt_schedule(void)
+{
+ if (!static_branch_unlikely(&sk_dynamic_preempt_schedule))
+ return;
+ preempt_schedule();
+}
+NOKPROBE_SYMBOL(dynamic_preempt_schedule);
+EXPORT_SYMBOL(dynamic_preempt_schedule);
+#endif
#endif
-
/**
* preempt_schedule_notrace - preempt_schedule called by tracing
@@ -6553,12 +6564,24 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#ifndef preempt_schedule_notrace_dynamic_enabled
#define preempt_schedule_notrace_dynamic_enabled preempt_schedule_notrace
#define preempt_schedule_notrace_dynamic_disabled NULL
#endif
DEFINE_STATIC_CALL(preempt_schedule_notrace, preempt_schedule_notrace_dynamic_enabled);
EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+static DEFINE_STATIC_KEY_TRUE(sk_dynamic_preempt_schedule_notrace);
+void __sched notrace dynamic_preempt_schedule_notrace(void)
+{
+ if (!static_branch_unlikely(&sk_dynamic_preempt_schedule_notrace))
+ return;
+ preempt_schedule_notrace();
+}
+NOKPROBE_SYMBOL(dynamic_preempt_schedule_notrace);
+EXPORT_SYMBOL(dynamic_preempt_schedule_notrace);
+#endif
#endif
#endif /* CONFIG_PREEMPTION */
@@ -8068,6 +8091,7 @@ EXPORT_SYMBOL(__cond_resched);
#endif
#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define cond_resched_dynamic_enabled __cond_resched
#define cond_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(cond_resched, __cond_resched);
@@ -8077,6 +8101,25 @@ EXPORT_STATIC_CALL_TRAMP(cond_resched);
#define might_resched_dynamic_disabled ((void *)&__static_call_return0)
DEFINE_STATIC_CALL_RET0(might_resched, __cond_resched);
EXPORT_STATIC_CALL_TRAMP(might_resched);
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+static DEFINE_STATIC_KEY_FALSE(sk_dynamic_cond_resched);
+int __sched dynamic_cond_resched(void)
+{
+ if (!static_branch_unlikely(&sk_dynamic_cond_resched))
+ return 0;
+ return __cond_resched();
+}
+EXPORT_SYMBOL(dynamic_cond_resched);
+
+static DEFINE_STATIC_KEY_FALSE(sk_dynamic_might_resched);
+int __sched dynamic_might_resched(void)
+{
+ if (!static_branch_unlikely(&sk_dynamic_might_resched))
+ return 0;
+ return __cond_resched();
+}
+EXPORT_SYMBOL(dynamic_might_resched);
+#endif
#endif
/*
@@ -8206,8 +8249,15 @@ int sched_dynamic_mode(const char *str)
return -EINVAL;
}
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
#define preempt_dynamic_enable(f) static_call_update(f, f##_dynamic_enabled)
#define preempt_dynamic_disable(f) static_call_update(f, f##_dynamic_disabled)
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+#define preempt_dynamic_enable(f) static_key_enable(&sk_dynamic_##f.key)
+#define preempt_dynamic_disable(f) static_key_disable(&sk_dynamic_##f.key)
+#else
+#error "Unsupported PREEMPT_DYNAMIC mechanism"
+#endif
void sched_dynamic_update(int mode)
{
Hi Mark,
Mark Rutland <[email protected]> writes:
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index 1739ca79613b..b145249ad91a 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -3,6 +3,7 @@
> #include <linux/context_tracking.h>
> #include <linux/entry-common.h>
> #include <linux/highmem.h>
> +#include <linux/jump_label.h>
> #include <linux/livepatch.h>
> #include <linux/audit.h>
> #include <linux/tick.h>
> @@ -392,7 +393,17 @@ void raw_irqentry_exit_cond_resched(void)
> }
> }
> #ifdef CONFIG_PREEMPT_DYNAMIC
> +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
> DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
> +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> +void dynamic_irqentry_exit_cond_resched(void)
> +{
> + if (!static_key_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> + return;
I think that should be static_branch_unlikely()?
Also can we make dynamic_irqentry_exit_cond_resched static so that the
compiler will inline it? I played a bit with your changes on s390 and
noticed the the compiler will generate an empty function. Declaring it
static inlines it and saves one unnecessary function call.
Thanks!
Sven