linux-kernel - Re: [PATCH v4 4/4] riscv: Improve flush_tlb_kernel

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Message-ID: <CAHVXubjYpkaOhP3oJwAQVHJLON7pNt+D0A7enqr3n5UuKC13UQ@mail.gmail.com>
Date:   Wed, 13 Sep 2023 10:32:13 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Will Deacon <will@...nel.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mayuresh Chitale <mchitale@...tanamicro.com>,
        Vincent Chen <vincent.chen@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Samuel Holland <samuel@...lland.org>,
        Andrew Jones <ajones@...tanamicro.com>
Subject: Re: [PATCH v4 4/4] riscv: Improve flush_tlb_kernel_range()

On Wed, Sep 13, 2023 at 10:24 AM Lad, Prabhakar
<prabhakar.csengg@...il.com> wrote:
>
> Hi Alexandre,
>
> On Wed, Sep 13, 2023 at 9:04 AM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
> >
> > @Lad, Prabhakar Any chance you give a try to this new patchset? So
> > that we make sure Samuel found your issue :)
> >
> I have given the patches a try and not seen the module load failures
> as seen previously. I have some rigorous tests which test the complete
> platform. I'm just waiting for it to complete before I give Tested by.
>

Awesome, thanks for the update! Well done @Samuel Holland

> Cheers,
> Prabhakar
>
> > On Mon, Sep 11, 2023 at 3:16 PM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
> > >
> > > This function used to simply flush the whole tlb of all harts, be more
> > > subtile and try to only flush the range.
> > >
> > > The problem is that we can only use PAGE_SIZE as stride since we don't know
> > > the size of the underlying mapping and then this function will be improved
> > > only if the size of the region to flush is < threshold * PAGE_SIZE.
> > >
> > > Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> > > Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
> > > ---
> > >  arch/riscv/include/asm/tlbflush.h | 11 ++++++-----
> > >  arch/riscv/mm/tlbflush.c          | 33 ++++++++++++++++++++++---------
> > >  2 files changed, 30 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
> > > index 170a49c531c6..8f3418c5f172 100644
> > > --- a/arch/riscv/include/asm/tlbflush.h
> > > +++ b/arch/riscv/include/asm/tlbflush.h
> > > @@ -40,6 +40,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
> > >  void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr);
> > >  void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
> > >                      unsigned long end);
> > > +void flush_tlb_kernel_range(unsigned long start, unsigned long end);
> > >  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > >  #define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
> > >  void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
> > > @@ -56,15 +57,15 @@ static inline void flush_tlb_range(struct vm_area_struct *vma,
> > >         local_flush_tlb_all();
> > >  }
> > >
> > > -#define flush_tlb_mm(mm) flush_tlb_all()
> > > -#define flush_tlb_mm_range(mm, start, end, page_size) flush_tlb_all()
> > > -#endif /* !CONFIG_SMP || !CONFIG_MMU */
> > > -
> > >  /* Flush a range of kernel pages */
> > >  static inline void flush_tlb_kernel_range(unsigned long start,
> > >         unsigned long end)
> > >  {
> > > -       flush_tlb_all();
> > > +       local_flush_tlb_all();
> > >  }
> > >
> > > +#define flush_tlb_mm(mm) flush_tlb_all()
> > > +#define flush_tlb_mm_range(mm, start, end, page_size) flush_tlb_all()
> > > +#endif /* !CONFIG_SMP || !CONFIG_MMU */
> > > +
> > >  #endif /* _ASM_RISCV_TLBFLUSH_H */
> > > diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> > > index 2c1136d73411..28cd8539b575 100644
> > > --- a/arch/riscv/mm/tlbflush.c
> > > +++ b/arch/riscv/mm/tlbflush.c
> > > @@ -97,19 +97,27 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
> > >                               unsigned long size, unsigned long stride)
> > >  {
> > >         struct flush_tlb_range_data ftd;
> > > -       struct cpumask *cmask = mm_cpumask(mm);
> > > +       struct cpumask *cmask, full_cmask;
> > >         unsigned long asid = FLUSH_TLB_NO_ASID;
> > > -       unsigned int cpuid;
> > >         bool broadcast;
> > >
> > > -       if (cpumask_empty(cmask))
> > > -               return;
> > > +       if (mm) {
> > > +               unsigned int cpuid;
> > > +
> > > +               cmask = mm_cpumask(mm);
> > > +               if (cpumask_empty(cmask))
> > > +                       return;
> > >
> > > -       cpuid = get_cpu();
> > > -       /* check if the tlbflush needs to be sent to other CPUs */
> > > -       broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
> > > +               cpuid = get_cpu();
> > > +               /* check if the tlbflush needs to be sent to other CPUs */
> > > +               broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
> > > +       } else {
> > > +               cpumask_setall(&full_cmask);
> > > +               cmask = &full_cmask;
> > > +               broadcast = true;
> > > +       }
> > >
> > > -       if (static_branch_unlikely(&use_asid_allocator))
> > > +       if (static_branch_unlikely(&use_asid_allocator) && mm)
> > >                 asid = atomic_long_read(&mm->context.id) & asid_mask;
> > >
> > >         if (broadcast) {
> > > @@ -128,7 +136,8 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
> > >                 local_flush_tlb_range_asid(start, size, stride, asid);
> > >         }
> > >
> > > -       put_cpu();
> > > +       if (mm)
> > > +               put_cpu();
> > >  }
> > >
> > >  void flush_tlb_mm(struct mm_struct *mm)
> > > @@ -189,6 +198,12 @@ void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
> > >
> > >         __flush_tlb_range(vma->vm_mm, start, end - start, stride_size);
> > >  }
> > > +
> > > +void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> > > +{
> > > +       __flush_tlb_range(NULL, start, end - start, PAGE_SIZE);
> > > +}
> > > +
> > >  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > >  void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
> > >                         unsigned long end)
> > > --
> > > 2.39.2
> > >