From: Alexander Gordeev <agordeev@linux.ibm.com>

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>
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.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 b0f200aba2b3..97f35f9b1a96 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 __ASSEMBLER__
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index eb23966ac0a9..9237dcbeee4a 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
-- 
2.47.0

On 29/10/2025 10:08, Kevin Brodsky wrote:
> From: Alexander Gordeev <agordeev@linux.ibm.com>
> 
> 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>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>

Reviewed-by: Ryan Roberts <ryan.roberts@arm.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 b0f200aba2b3..97f35f9b1a96 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 __ASSEMBLER__
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index eb23966ac0a9..9237dcbeee4a 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

On 07/11/2025 12:25, Ryan Roberts wrote:
> On 29/10/2025 10:08, Kevin Brodsky wrote:
>> From: Alexander Gordeev <agordeev@linux.ibm.com>
>>
>> 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>
>> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
> 
> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>

I should also add, that as far as I can tell, this was dead code because the
powerpc implementation disables preemption in a lazy mmu region. It would
probably be preferable to understand why the preemption disabling approach was
added in the first place. Perhaps it would be better to remove that and keep
this code. But given you are not changing any current behaviour and this is
removing dead code, that's probably something for the ppc folks to look into
another day.

Thanks,
Ryan

> 
>> ---
>>  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 b0f200aba2b3..97f35f9b1a96 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 __ASSEMBLER__
>> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
>> index eb23966ac0a9..9237dcbeee4a 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
>

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

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

Since the commit referenced in above disables the preemption in
arch_enter_lazy_mmu(), so the expectation is that we will never be
context switched while in lazy_mmu, hence the code changes in
switch_to() around __flush_tlb_pending() should ideally never be called.

With this analysis - the patch looks good to me. I will give this entire
patch series a try on Power HW with Hash mmu too (which uses lazy mmu and
let you know the results of that)!

For this patch please feel free to add:
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>


CC: Venkat who also runs CI on linux Power HW for upstream testing :)

-ritesh


> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> index b0f200aba2b3..97f35f9b1a96 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 __ASSEMBLER__
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index eb23966ac0a9..9237dcbeee4a 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
> -- 
> 2.47.0

On 05/11/2025 02:46, Ritesh Harjani (IBM) wrote:
> Kevin Brodsky <kevin.brodsky@arm.com> writes:
>
>> From: Alexander Gordeev <agordeev@linux.ibm.com>
>>
>> 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>
>> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
>> ---
>>  arch/powerpc/include/asm/thread_info.h |  2 --
>>  arch/powerpc/kernel/process.c          | 25 -------------------------
>>  2 files changed, 27 deletions(-)
>>
> Since the commit referenced in above disables the preemption in
> arch_enter_lazy_mmu(), so the expectation is that we will never be
> context switched while in lazy_mmu, hence the code changes in
> switch_to() around __flush_tlb_pending() should ideally never be called.

Correct, that's the idea.

> With this analysis - the patch looks good to me. I will give this entire
> patch series a try on Power HW with Hash mmu too (which uses lazy mmu and
> let you know the results of that)!

That'd be very appreciated, thanks a lot!

> For this patch please feel free to add:
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
>
>
> CC: Venkat who also runs CI on linux Power HW for upstream testing :)

Ack, will Cc you both in the next version.

- Kevin

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

> On 05/11/2025 02:46, Ritesh Harjani (IBM) wrote:
>> Kevin Brodsky <kevin.brodsky@arm.com> writes:
>>
>>> From: Alexander Gordeev <agordeev@linux.ibm.com>
>>>
>>> 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>
>>> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
>>> ---
>>>  arch/powerpc/include/asm/thread_info.h |  2 --
>>>  arch/powerpc/kernel/process.c          | 25 -------------------------
>>>  2 files changed, 27 deletions(-)
>>>
>> Since the commit referenced in above disables the preemption in
>> arch_enter_lazy_mmu(), so the expectation is that we will never be
>> context switched while in lazy_mmu, hence the code changes in
>> switch_to() around __flush_tlb_pending() should ideally never be called.
>
> Correct, that's the idea.
>
>> With this analysis - the patch looks good to me. I will give this entire
>> patch series a try on Power HW with Hash mmu too (which uses lazy mmu and
>> let you know the results of that)!
>
> That'd be very appreciated, thanks a lot!
>

I did give this patch series a run on Power10 with Hash MMU. I ran the
following stress-ng tests and didn't observe any issues (kernel warnings) so far.

stress-ng --all 0 -t 60s --perf -v --verify \
--tlb-shootdown 0 \
--fault 0 \
--userfaultfd 0 \
--fork 0 \
--exec 0 \
--memfd 0 \
--numa 0 \
--pkey 0 \
--remap 0 \
--vm 0 \
--rmap 0 \
-x swap,pagemove
(Note not all options shown here will work with --verify)

Let me know what else I can run for validation?
Do you know of any specific tests for validation of lazy mmu feature?

>> For this patch please feel free to add:
>> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
>>
>>
>> CC: Venkat who also runs CI on linux Power HW for upstream testing :)
>
> Ack, will Cc you both in the next version.

Sure. Thanks!

-ritesh

On 08/11/2025 00:35, Ritesh Harjani (IBM) wrote:
> Kevin Brodsky <kevin.brodsky@arm.com> writes:
>
>> [...]
>>
>>> With this analysis - the patch looks good to me. I will give this entire
>>> patch series a try on Power HW with Hash mmu too (which uses lazy mmu and
>>> let you know the results of that)!
>> That'd be very appreciated, thanks a lot!
>>
> I did give this patch series a run on Power10 with Hash MMU. I ran the
> following stress-ng tests and didn't observe any issues (kernel warnings) so far.
>
> stress-ng --all 0 -t 60s --perf -v --verify \
> --tlb-shootdown 0 \
> --fault 0 \
> --userfaultfd 0 \
> --fork 0 \
> --exec 0 \
> --memfd 0 \
> --numa 0 \
> --pkey 0 \
> --remap 0 \
> --vm 0 \
> --rmap 0 \
> -x swap,pagemove
> (Note not all options shown here will work with --verify)

That's great, many thanks!

> Let me know what else I can run for validation?
> Do you know of any specific tests for validation of lazy mmu feature?

I don't think there is - lazy MMU is not supposed to have any observable
effect, all we can do is exercise the paths that use it and check that
nothing explodes.

That said it wouldn't hurt to run the mm kselftests:

    make -C tools/testing/selftests/ TARGETS=mm

Thanks!

- Kevin

On 29.10.25 11:08, Kevin Brodsky wrote:
> From: Alexander Gordeev <agordeev@linux.ibm.com>
> 
> 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>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
> ---

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb