Re: [PATCH v5 18/25] arm64/mm: Split __flush_tlb_range() to elide trailing DSB

David Hildenbrand
2024-02-12T13:15:08Z

On 12.02.24 14:05, Ryan Roberts wrote:
> On 12/02/2024 12:44, David Hildenbrand wrote:
>> On 02.02.24 09:07, Ryan Roberts wrote:
>>> Split __flush_tlb_range() into __flush_tlb_range_nosync() +
>>> __flush_tlb_range(), in the same way as the existing flush_tlb_page()
>>> arrangement. This allows calling __flush_tlb_range_nosync() to elide the
>>> trailing DSB. Forthcoming "contpte" code will take advantage of this
>>> when clearing the young bit from a contiguous range of ptes.
>>>
>>> Tested-by: John Hubbard <jhubbard@nvidia.com>
>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>>> ---
>>>   arch/arm64/include/asm/tlbflush.h | 13 +++++++++++--
>>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/tlbflush.h
>>> b/arch/arm64/include/asm/tlbflush.h
>>> index 79e932a1bdf8..50a765917327 100644
>>> --- a/arch/arm64/include/asm/tlbflush.h
>>> +++ b/arch/arm64/include/asm/tlbflush.h
>>> @@ -422,7 +422,7 @@ do {                                    \
>>>   #define __flush_s2_tlb_range_op(op, start, pages, stride, tlb_level) \
>>>       __flush_tlb_range_op(op, start, pages, stride, 0, tlb_level, false,
>>> kvm_lpa2_is_enabled());
>>>   -static inline void __flush_tlb_range(struct vm_area_struct *vma,
>>> +static inline void __flush_tlb_range_nosync(struct vm_area_struct *vma,
>>>                        unsigned long start, unsigned long end,
>>>                        unsigned long stride, bool last_level,
>>>                        int tlb_level)
>>> @@ -456,10 +456,19 @@ static inline void __flush_tlb_range(struct
>>> vm_area_struct *vma,
>>>           __flush_tlb_range_op(vae1is, start, pages, stride, asid,
>>>                        tlb_level, true, lpa2_is_enabled());
>>>   -    dsb(ish);
>>>       mmu_notifier_arch_invalidate_secondary_tlbs(vma->vm_mm, start, end);
>>>   }
>>>   +static inline void __flush_tlb_range(struct vm_area_struct *vma,
>>> +                     unsigned long start, unsigned long end,
>>> +                     unsigned long stride, bool last_level,
>>> +                     int tlb_level)
>>> +{
>>> +    __flush_tlb_range_nosync(vma, start, end, stride,
>>> +                 last_level, tlb_level);
>>> +    dsb(ish);
>>> +}
>>> +
>>>   static inline void flush_tlb_range(struct vm_area_struct *vma,
>>>                      unsigned long start, unsigned long end)
>>>   {
>>
>> You're now calling dsb() after mmu_notifier_arch_invalidate_secondary_tlbs().
>>
>>
>> In flush_tlb_mm(), we have the order
>>
>>     dsb(ish);
>>     mmu_notifier_arch_invalidate_secondary_tlbs()
>>
>> In flush_tlb_page(), we have the effective order:
>>
>>     mmu_notifier_arch_invalidate_secondary_tlbs()
>>     dsb(ish);
>>
>> In flush_tlb_range(), we used to have the order:
>>
>>     dsb(ish);
>>     mmu_notifier_arch_invalidate_secondary_tlbs();
>>
>>
>> So I *suspect* having that DSB before
>> mmu_notifier_arch_invalidate_secondary_tlbs() is fine. Hopefully, nothing in
>> there relies on that placement.
>
> Will spotted this against v3. My argument was that I was following the existing
> pattern in flush_tlb_page(). Apparently that is not correct and needs changing,
> but the conclusion was to leave my change as is for now, since it is consistent
> and change them at a later date together.

Good, I think you should add a few words to the patch description
("ordering might be incorrect, but is in-line with __flush_tlb_page()";
will be resolved separately).

--
Cheers,

David / dhildenb