[v4] Nesting support for lazy MMU mode

[PATCH v4 09/12] powerpc/mm: replace batch->active with in_lazy_mmu_mode()

Posted by Kevin Brodsky 1 month, 2 weeks ago

A per-CPU batch struct is activated when entering lazy MMU mode; its
lifetime is the same as the lazy MMU section (it is deactivated when
leaving the mode). Preemption is disabled in that interval to ensure
that the per-CPU reference remains valid.

The generic lazy_mmu layer now tracks whether a task is in lazy MMU
mode. We can therefore use the generic helper in_lazy_mmu_mode()
to tell whether a batch struct is active instead of tracking it
explicitly.

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
 arch/powerpc/include/asm/book3s/64/tlbflush-hash.h | 9 ---------
 arch/powerpc/mm/book3s64/hash_tlb.c                | 2 +-
 2 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
index 623a8a8b2d0e..bbc54690d374 100644
--- a/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
+++ b/arch/powerpc/include/asm/book3s/64/tlbflush-hash.h
@@ -12,7 +12,6 @@
 #define PPC64_TLB_BATCH_NR 192
 
 struct ppc64_tlb_batch {
-	int			active;
 	unsigned long		index;
 	struct mm_struct	*mm;
 	real_pte_t		pte[PPC64_TLB_BATCH_NR];
@@ -26,8 +25,6 @@ extern void __flush_tlb_pending(struct ppc64_tlb_batch *batch);
 
 static inline void arch_enter_lazy_mmu_mode(void)
 {
-	struct ppc64_tlb_batch *batch;
-
 	if (radix_enabled())
 		return;
 	/*
@@ -35,8 +32,6 @@ static inline void arch_enter_lazy_mmu_mode(void)
 	 * operating on kernel page tables.
 	 */
 	preempt_disable();
-	batch = this_cpu_ptr(&ppc64_tlb_batch);
-	batch->active = 1;
 }
 
 static inline void arch_flush_lazy_mmu_mode(void)
@@ -51,14 +46,10 @@ static inline void arch_flush_lazy_mmu_mode(void)
 
 static inline void arch_leave_lazy_mmu_mode(void)
 {
-	struct ppc64_tlb_batch *batch;
-
 	if (radix_enabled())
 		return;
-	batch = this_cpu_ptr(&ppc64_tlb_batch);
 
 	arch_flush_lazy_mmu_mode();
-	batch->active = 0;
 	preempt_enable();
 }
 
diff --git a/arch/powerpc/mm/book3s64/hash_tlb.c b/arch/powerpc/mm/book3s64/hash_tlb.c
index 787f7a0e27f0..72b83f582b6d 100644
--- a/arch/powerpc/mm/book3s64/hash_tlb.c
+++ b/arch/powerpc/mm/book3s64/hash_tlb.c
@@ -100,7 +100,7 @@ void hpte_need_flush(struct mm_struct *mm, unsigned long addr,
 	 * Check if we have an active batch on this CPU. If not, just
 	 * flush now and return.
 	 */
-	if (!batch->active) {
+	if (!in_lazy_mmu_mode()) {
 		flush_hash_page(vpn, rpte, psize, ssize, mm_is_thread_local(mm));
 		put_cpu_var(ppc64_tlb_batch);
 		return;
-- 
2.47.0

Re: [PATCH v4 09/12] powerpc/mm: replace batch->active with in_lazy_mmu_mode()

Posted by Ritesh Harjani (IBM) 1 month, 1 week ago

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

> A per-CPU batch struct is activated when entering lazy MMU mode; its
> lifetime is the same as the lazy MMU section (it is deactivated when
> leaving the mode). Preemption is disabled in that interval to ensure
> that the per-CPU reference remains valid.
>
> The generic lazy_mmu layer now tracks whether a task is in lazy MMU
> mode. We can therefore use the generic helper in_lazy_mmu_mode()
> to tell whether a batch struct is active instead of tracking it
> explicitly.
>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
> ---
>  arch/powerpc/include/asm/book3s/64/tlbflush-hash.h | 9 ---------
>  arch/powerpc/mm/book3s64/hash_tlb.c                | 2 +-
>  2 files changed, 1 insertion(+), 10 deletions(-)
>

This looks good to me.

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

Re: [PATCH v4 09/12] powerpc/mm: replace batch->active with in_lazy_mmu_mode()

Posted by David Hildenbrand 1 month, 1 week ago

On 29.10.25 11:09, Kevin Brodsky wrote:
> A per-CPU batch struct is activated when entering lazy MMU mode; its
> lifetime is the same as the lazy MMU section (it is deactivated when
> leaving the mode). Preemption is disabled in that interval to ensure
> that the per-CPU reference remains valid.
> 
> The generic lazy_mmu layer now tracks whether a task is in lazy MMU
> mode. We can therefore use the generic helper in_lazy_mmu_mode()
> to tell whether a batch struct is active instead of tracking it
> explicitly.
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
> ---

I suspect you were not able to test this on real HW. Some help from the 
ppc folks would be appreciated.

LGTM, but the interaction with pause/resume adds a bit of complication 
on top.

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

-- 
Cheers

David

Re: [PATCH v4 09/12] powerpc/mm: replace batch->active with in_lazy_mmu_mode()

Posted by Kevin Brodsky 1 month, 1 week ago

On 03/11/2025 16:05, David Hildenbrand wrote:
> On 29.10.25 11:09, Kevin Brodsky wrote:
>> A per-CPU batch struct is activated when entering lazy MMU mode; its
>> lifetime is the same as the lazy MMU section (it is deactivated when
>> leaving the mode). Preemption is disabled in that interval to ensure
>> that the per-CPU reference remains valid.
>>
>> The generic lazy_mmu layer now tracks whether a task is in lazy MMU
>> mode. We can therefore use the generic helper in_lazy_mmu_mode()
>> to tell whether a batch struct is active instead of tracking it
>> explicitly.
>>
>> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
>> ---
>
> I suspect you were not able to test this on real HW. Some help from
> the ppc folks would be appreciated.

Indeed, it would be nice to get some testing on ppc HW that actually
uses lazy MMU (!radix_enabled()).

>
> LGTM, but the interaction with pause/resume adds a bit of complication
> on top.

Does it? This series doesn't change when arch_enter() and arch_leave()
are called, batch->active and in_lazy_mmu_mode() should coincide. 

- Kevin