* [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability
@ 2022-01-27 19:24 Valentin Schneider
2022-02-04 9:29 ` Sebastian Andrzej Siewior
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: Valentin Schneider @ 2022-01-27 19:24 UTC (permalink / raw)
To: linux-kernel, linux-arm-kernel, linux-rt-users
Cc: Sebastian Andrzej Siewior, Catalin Marinas, Will Deacon,
Ingo Molnar, Peter Zijlstra, Thomas Gleixner, Steven Rostedt,
Daniel Bristot de Oliveira, Paul E. McKenney, Frederic Weisbecker,
Josh Triplett, Mathieu Desnoyers, Davidlohr Bueso, Lai Jiangshan,
Joel Fernandes, Anshuman Khandual, Vincenzo Frascino,
Steven Price, Ard Biesheuvel, Boqun Feng, Mike Galbraith
arch_faults_on_old_pte() relies on the calling context being
non-preemptible. CONFIG_PREEMPT_RT turns the PTE lock into a sleepable
spinlock, which doesn't disable preemption once acquired, triggering the
warning in arch_faults_on_old_pte().
It does however disable migration, ensuring the task remains on the same
CPU during the entirety of the critical section, making the read of
cpu_has_hw_af() safe and stable.
Make arch_faults_on_old_pte() check cant_migrate() instead of preemptible().
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lore.kernel.org/r/20210811201354.1976839-5-valentin.schneider@arm.com
---
v3 -> v4: Dropped migratable(), reuse cant_migrate() (Sebastian)
---
arch/arm64/include/asm/pgtable.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index c4ba047a82d2..3caf6346ea95 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -1001,7 +1001,8 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
*/
static inline bool arch_faults_on_old_pte(void)
{
- WARN_ON(preemptible());
+ /* The register read below requires a stable CPU to make any sense */
+ cant_migrate();
return !cpu_has_hw_af();
}
--
2.25.1
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^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability
2022-01-27 19:24 [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability Valentin Schneider
@ 2022-02-04 9:29 ` Sebastian Andrzej Siewior
2022-02-04 18:55 ` Catalin Marinas
2022-02-15 15:37 ` Will Deacon
2 siblings, 0 replies; 5+ messages in thread
From: Sebastian Andrzej Siewior @ 2022-02-04 9:29 UTC (permalink / raw)
To: Valentin Schneider
Cc: linux-kernel, linux-arm-kernel, linux-rt-users, Catalin Marinas,
Will Deacon, Ingo Molnar, Peter Zijlstra, Thomas Gleixner,
Steven Rostedt, Daniel Bristot de Oliveira, Paul E. McKenney,
Frederic Weisbecker, Josh Triplett, Mathieu Desnoyers,
Davidlohr Bueso, Lai Jiangshan, Joel Fernandes, Anshuman Khandual,
Vincenzo Frascino, Steven Price, Ard Biesheuvel, Boqun Feng,
Mike Galbraith
On 2022-01-27 19:24:37 [+0000], Valentin Schneider wrote:
> arch_faults_on_old_pte() relies on the calling context being
> non-preemptible. CONFIG_PREEMPT_RT turns the PTE lock into a sleepable
> spinlock, which doesn't disable preemption once acquired, triggering the
> warning in arch_faults_on_old_pte().
>
> It does however disable migration, ensuring the task remains on the same
> CPU during the entirety of the critical section, making the read of
> cpu_has_hw_af() safe and stable.
>
> Make arch_faults_on_old_pte() check cant_migrate() instead of preemptible().
>
> Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Link: https://lore.kernel.org/r/20210811201354.1976839-5-valentin.schneider@arm.com
Let me pick that up so I can drop the other two. I hope the ARM64 folks
follow my lead ;)
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Sebastian
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability
2022-01-27 19:24 [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability Valentin Schneider
2022-02-04 9:29 ` Sebastian Andrzej Siewior
@ 2022-02-04 18:55 ` Catalin Marinas
2022-02-04 19:09 ` Sebastian Andrzej Siewior
2022-02-15 15:37 ` Will Deacon
2 siblings, 1 reply; 5+ messages in thread
From: Catalin Marinas @ 2022-02-04 18:55 UTC (permalink / raw)
To: Valentin Schneider
Cc: linux-kernel, linux-arm-kernel, linux-rt-users,
Sebastian Andrzej Siewior, Will Deacon, Ingo Molnar,
Peter Zijlstra, Thomas Gleixner, Steven Rostedt,
Daniel Bristot de Oliveira, Paul E. McKenney, Frederic Weisbecker,
Josh Triplett, Mathieu Desnoyers, Davidlohr Bueso, Lai Jiangshan,
Joel Fernandes, Anshuman Khandual, Vincenzo Frascino,
Steven Price, Ard Biesheuvel, Boqun Feng, Mike Galbraith
On Thu, Jan 27, 2022 at 07:24:37PM +0000, Valentin Schneider wrote:
> arch_faults_on_old_pte() relies on the calling context being
> non-preemptible. CONFIG_PREEMPT_RT turns the PTE lock into a sleepable
> spinlock, which doesn't disable preemption once acquired, triggering the
> warning in arch_faults_on_old_pte().
>
> It does however disable migration, ensuring the task remains on the same
> CPU during the entirety of the critical section, making the read of
> cpu_has_hw_af() safe and stable.
>
> Make arch_faults_on_old_pte() check cant_migrate() instead of preemptible().
>
> Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Link: https://lore.kernel.org/r/20210811201354.1976839-5-valentin.schneider@arm.com
> ---
> v3 -> v4: Dropped migratable(), reuse cant_migrate() (Sebastian)
> ---
> arch/arm64/include/asm/pgtable.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index c4ba047a82d2..3caf6346ea95 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -1001,7 +1001,8 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
> */
> static inline bool arch_faults_on_old_pte(void)
> {
> - WARN_ON(preemptible());
> + /* The register read below requires a stable CPU to make any sense */
> + cant_migrate();
>
> return !cpu_has_hw_af();
> }
The patch looks alright but what's the plan with it? Does it go into the
preempt-rt tree, mainline? It's not a fix to be queued now, so:
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability
2022-02-04 18:55 ` Catalin Marinas
@ 2022-02-04 19:09 ` Sebastian Andrzej Siewior
0 siblings, 0 replies; 5+ messages in thread
From: Sebastian Andrzej Siewior @ 2022-02-04 19:09 UTC (permalink / raw)
To: Catalin Marinas
Cc: Valentin Schneider, linux-kernel, linux-arm-kernel,
linux-rt-users, Will Deacon, Ingo Molnar, Peter Zijlstra,
Thomas Gleixner, Steven Rostedt, Daniel Bristot de Oliveira,
Paul E. McKenney, Frederic Weisbecker, Josh Triplett,
Mathieu Desnoyers, Davidlohr Bueso, Lai Jiangshan, Joel Fernandes,
Anshuman Khandual, Vincenzo Frascino, Steven Price,
Ard Biesheuvel, Boqun Feng, Mike Galbraith
On 2022-02-04 18:55:17 [+0000], Catalin Marinas wrote:
>
> The patch looks alright but what's the plan with it? Does it go into the
> preempt-rt tree, mainline? It's not a fix to be queued now, so:
It would be nice if if it could go mainline, too.
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Sebastian
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability
2022-01-27 19:24 [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability Valentin Schneider
2022-02-04 9:29 ` Sebastian Andrzej Siewior
2022-02-04 18:55 ` Catalin Marinas
@ 2022-02-15 15:37 ` Will Deacon
2 siblings, 0 replies; 5+ messages in thread
From: Will Deacon @ 2022-02-15 15:37 UTC (permalink / raw)
To: Valentin Schneider
Cc: linux-kernel, linux-arm-kernel, linux-rt-users,
Sebastian Andrzej Siewior, Catalin Marinas, Ingo Molnar,
Peter Zijlstra, Thomas Gleixner, Steven Rostedt,
Daniel Bristot de Oliveira, Paul E. McKenney, Frederic Weisbecker,
Josh Triplett, Mathieu Desnoyers, Davidlohr Bueso, Lai Jiangshan,
Joel Fernandes, Anshuman Khandual, Vincenzo Frascino,
Steven Price, Ard Biesheuvel, Boqun Feng, Mike Galbraith
On Thu, Jan 27, 2022 at 07:24:37PM +0000, Valentin Schneider wrote:
> arch_faults_on_old_pte() relies on the calling context being
> non-preemptible. CONFIG_PREEMPT_RT turns the PTE lock into a sleepable
> spinlock, which doesn't disable preemption once acquired, triggering the
> warning in arch_faults_on_old_pte().
>
> It does however disable migration, ensuring the task remains on the same
> CPU during the entirety of the critical section, making the read of
> cpu_has_hw_af() safe and stable.
>
> Make arch_faults_on_old_pte() check cant_migrate() instead of preemptible().
>
> Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Link: https://lore.kernel.org/r/20210811201354.1976839-5-valentin.schneider@arm.com
> ---
> v3 -> v4: Dropped migratable(), reuse cant_migrate() (Sebastian)
> ---
> arch/arm64/include/asm/pgtable.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index c4ba047a82d2..3caf6346ea95 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -1001,7 +1001,8 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
> */
> static inline bool arch_faults_on_old_pte(void)
> {
> - WARN_ON(preemptible());
> + /* The register read below requires a stable CPU to make any sense */
> + cant_migrate();
FWIW: There's a patch in the multi-generational LRU series that drops this
WARN_ON() entirely. I'm not sure if/when that lot will land, but just wanted
to let you know.
Will
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^ permalink raw reply [flat|nested] 5+ messages in thread
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2022-01-27 19:24 [PATCH v4] arm64: mm: Make arch_faults_on_old_pte() check for migratability Valentin Schneider
2022-02-04 9:29 ` Sebastian Andrzej Siewior
2022-02-04 18:55 ` Catalin Marinas
2022-02-04 19:09 ` Sebastian Andrzej Siewior
2022-02-15 15:37 ` Will Deacon
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