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

[David Hildenbrand]

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@xxxxxxxxxx>
> > > Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
> > > ---
> > >    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