mm: Consolidate lazy MMU mode context

[PATCH 6/6] powerpc/64s: Do not re-activate batched TLB flush

Posted by Alexander Gordeev 4 months ago

Since commit b9ef323ea168 ("powerpc/64s: Disable preemption in hash
lazy mmu mode") a task can not be preempted while in lazy MMU mode.
Therefore, the batch re-activation code is never called, so remove it.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
---
 arch/powerpc/include/asm/thread_info.h |  2 --
 arch/powerpc/kernel/process.c          | 25 -------------------------
 2 files changed, 27 deletions(-)

diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 2785c7462ebf..092118a68862 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -154,12 +154,10 @@ void arch_setup_new_exec(void);
 /* Don't move TLF_NAPPING without adjusting the code in entry_32.S */
 #define TLF_NAPPING		0	/* idle thread enabled NAP mode */
 #define TLF_SLEEPING		1	/* suspend code enabled SLEEP mode */
-#define TLF_LAZY_MMU		3	/* tlb_batch is active */
 #define TLF_RUNLATCH		4	/* Is the runlatch enabled? */
 
 #define _TLF_NAPPING		(1 << TLF_NAPPING)
 #define _TLF_SLEEPING		(1 << TLF_SLEEPING)
-#define _TLF_LAZY_MMU		(1 << TLF_LAZY_MMU)
 #define _TLF_RUNLATCH		(1 << TLF_RUNLATCH)
 
 #ifndef __ASSEMBLY__
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 855e09886503..edb59a447149 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1281,9 +1281,6 @@ struct task_struct *__switch_to(struct task_struct *prev,
 {
 	struct thread_struct *new_thread, *old_thread;
 	struct task_struct *last;
-#ifdef CONFIG_PPC_64S_HASH_MMU
-	struct ppc64_tlb_batch *batch;
-#endif
 
 	new_thread = &new->thread;
 	old_thread = &current->thread;
@@ -1291,14 +1288,6 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	WARN_ON(!irqs_disabled());
 
 #ifdef CONFIG_PPC_64S_HASH_MMU
-	batch = this_cpu_ptr(&ppc64_tlb_batch);
-	if (batch->active) {
-		current_thread_info()->local_flags |= _TLF_LAZY_MMU;
-		if (batch->index)
-			__flush_tlb_pending(batch);
-		batch->active = 0;
-	}
-
 	/*
 	 * On POWER9 the copy-paste buffer can only paste into
 	 * foreign real addresses, so unprivileged processes can not
@@ -1369,20 +1358,6 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	 */
 
 #ifdef CONFIG_PPC_BOOK3S_64
-#ifdef CONFIG_PPC_64S_HASH_MMU
-	/*
-	 * This applies to a process that was context switched while inside
-	 * arch_enter_lazy_mmu_mode(), to re-activate the batch that was
-	 * deactivated above, before _switch(). This will never be the case
-	 * for new tasks.
-	 */
-	if (current_thread_info()->local_flags & _TLF_LAZY_MMU) {
-		current_thread_info()->local_flags &= ~_TLF_LAZY_MMU;
-		batch = this_cpu_ptr(&ppc64_tlb_batch);
-		batch->active = 1;
-	}
-#endif
-
 	/*
 	 * Math facilities are masked out of the child MSR in copy_thread.
 	 * A new task does not need to restore_math because it will
-- 
2.48.1

Re: [PATCH 6/6] powerpc/64s: Do not re-activate batched TLB flush

Posted by Alexander Gordeev 3 months, 3 weeks ago

On Thu, Jun 12, 2025 at 07:36:13PM +0200, Alexander Gordeev wrote:
> Since commit b9ef323ea168 ("powerpc/64s: Disable preemption in hash
> lazy mmu mode") a task can not be preempted while in lazy MMU mode.
> Therefore, the batch re-activation code is never called, so remove it.
> 
> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
> ---
>  arch/powerpc/include/asm/thread_info.h |  2 --
>  arch/powerpc/kernel/process.c          | 25 -------------------------
>  2 files changed, 27 deletions(-)

Hi All,

(I trimmed non-ppc mailing lists/people).

The whole series does not seem to make it, but this patch alone is still
applicable and makes sence, if I am not mistaken.

Thanks!

Re: [PATCH 6/6] powerpc/64s: Do not re-activate batched TLB flush

Posted by Kevin Brodsky 1 week ago

On 17/06/2025 17:11, Alexander Gordeev wrote:
> On Thu, Jun 12, 2025 at 07:36:13PM +0200, Alexander Gordeev wrote:
>> Since commit b9ef323ea168 ("powerpc/64s: Disable preemption in hash
>> lazy mmu mode") a task can not be preempted while in lazy MMU mode.
>> Therefore, the batch re-activation code is never called, so remove it.
>>
>> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
>> ---
>>  arch/powerpc/include/asm/thread_info.h |  2 --
>>  arch/powerpc/kernel/process.c          | 25 -------------------------
>>  2 files changed, 27 deletions(-)
> Hi All,
>
> (I trimmed non-ppc mailing lists/people).
>
> The whole series does not seem to make it, but this patch alone is still
> applicable and makes sence, if I am not mistaken.

Yes, I agree. I arrived at the same conclusion working on the next
version of the nested lazy_mmu series [1]. May I include this patch in v3?

- Kevin

[1]
https://lore.kernel.org/all/20250908073931.4159362-1-kevin.brodsky@arm.com/

Re: [PATCH 6/6] powerpc/64s: Do not re-activate batched TLB flush

Posted by Ritesh Harjani (IBM) 3 days, 11 hours ago

Kevin Brodsky <kevin.brodsky@arm.com> writes:

> On 17/06/2025 17:11, Alexander Gordeev wrote:
>> On Thu, Jun 12, 2025 at 07:36:13PM +0200, Alexander Gordeev wrote:
>>> Since commit b9ef323ea168 ("powerpc/64s: Disable preemption in hash
>>> lazy mmu mode") a task can not be preempted while in lazy MMU mode.
>>> Therefore, the batch re-activation code is never called, so remove it.
>>>
>>> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
>>> ---
>>>  arch/powerpc/include/asm/thread_info.h |  2 --
>>>  arch/powerpc/kernel/process.c          | 25 -------------------------
>>>  2 files changed, 27 deletions(-)
>> Hi All,
>>
>> (I trimmed non-ppc mailing lists/people).
>>
>> The whole series does not seem to make it, but this patch alone is still
>> applicable and makes sence, if I am not mistaken.
>
> Yes, I agree. I arrived at the same conclusion working on the next
> version of the nested lazy_mmu series [1].
> [1]
> https://lore.kernel.org/all/20250908073931.4159362-1-kevin.brodsky@arm.com/

Yes, we disable preemption while in lazy mmu mode for Hash, so I agree that
we won't call into __switch_to() in between preempt_disable()/_enable().
So it does look like that we don't need that code. 


> May I include this patch in v3?
>

That should be ok. 

> - Kevin

Thanks!

-ritesh

Re: [PATCH 6/6] powerpc/64s: Do not re-activate batched TLB flush

Posted by Kevin Brodsky 3 days, 6 hours ago

On 07/10/2025 11:40, Ritesh Harjani (IBM) wrote:
> Kevin Brodsky <kevin.brodsky@arm.com> writes:
>
>> On 17/06/2025 17:11, Alexander Gordeev wrote:
>>> On Thu, Jun 12, 2025 at 07:36:13PM +0200, Alexander Gordeev wrote:
>>>> Since commit b9ef323ea168 ("powerpc/64s: Disable preemption in hash
>>>> lazy mmu mode") a task can not be preempted while in lazy MMU mode.
>>>> Therefore, the batch re-activation code is never called, so remove it.
>>>>
>>>> Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>
>>>> ---
>>>>  arch/powerpc/include/asm/thread_info.h |  2 --
>>>>  arch/powerpc/kernel/process.c          | 25 -------------------------
>>>>  2 files changed, 27 deletions(-)
>>> Hi All,
>>>
>>> (I trimmed non-ppc mailing lists/people).
>>>
>>> The whole series does not seem to make it, but this patch alone is still
>>> applicable and makes sence, if I am not mistaken.
>> Yes, I agree. I arrived at the same conclusion working on the next
>> version of the nested lazy_mmu series [1].
>> [1]
>> https://lore.kernel.org/all/20250908073931.4159362-1-kevin.brodsky@arm.com/
> Yes, we disable preemption while in lazy mmu mode for Hash, so I agree that
> we won't call into __switch_to() in between preempt_disable()/_enable().
> So it does look like that we don't need that code.

Thanks for confirming.

>> May I include this patch in v3?
>>
> That should be ok.

Thanks!

- Kevin