linux-kernel - Re: [PATCH v3 4/4] riscv: Improve flush_tlb_kernel

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Date:   Wed, 06 Sep 2023 06:16:10 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     alexghiti@...osinc.com
CC:     prabhakar.csengg@...il.com, geert+renesas@...der.be,
        Will Deacon <will@...nel.org>, aneesh.kumar@...ux.ibm.com,
        akpm@...ux-foundation.org, npiggin@...il.com, peterz@...radead.org,
        mchitale@...tanamicro.com, vincent.chen@...ive.com,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, ajones@...tanamicro.com
Subject:     Re: [PATCH v3 4/4] riscv: Improve flush_tlb_kernel_range()

On Wed, 06 Sep 2023 05:43:46 PDT (-0700), alexghiti@...osinc.com wrote:
> On Wed, Sep 6, 2023 at 2:24 PM Lad, Prabhakar
> <prabhakar.csengg@...il.com> wrote:
>>
>> Hi Alexandre,
>>
>> On Wed, Sep 6, 2023 at 1:18 PM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
>> >
>> > On Wed, Sep 6, 2023 at 2:09 PM Lad, Prabhakar
>> > <prabhakar.csengg@...il.com> wrote:
>> > >
>> > > Hi Alexandre,
>> > >
>> > > On Wed, Sep 6, 2023 at 1:01 PM Alexandre Ghiti <alexghiti@...osinc.com> wrote:
>> > > >
>> > > > Hi Prabhakar,
>> > > >
>> > > > On Wed, Sep 6, 2023 at 1:49 PM Lad, Prabhakar
>> > > > <prabhakar.csengg@...il.com> wrote:
>> > > > >
>> > > > > Hi Alexandre,
>> > > > >
>> > > > > On Tue, Aug 1, 2023 at 9:58 AM 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          | 34 +++++++++++++++++++++++--------
>> > > > > >  2 files changed, 31 insertions(+), 14 deletions(-)
>> > > > > >
>> > > > > After applying this patch, I am seeing module load issues on RZ/Five
>> > > > > (complete log [0]). I am testing defconfig + [1] (rz/five related
>> > > > > configs).
>> > > > >
>> > > > > Any pointers on what could be an issue here?
>> > > >
>> > > > Can you give me the exact version of the kernel you use? The trap
>> > > > addresses are vmalloc addresses, and a fix for those landed very late
>> > > > in the release cycle.
>> > > >
>> > > I am using next-20230906, Ive pushed a branch [1] for you to have a look.
>> > >
>> > > [0] https://github.com/prabhakarlad/linux/tree/rzfive-debug
>> >
>> > Great, thanks, I had to get rid of this possibility :)
>> >
>> > As-is, I have no idea, can you try to "bisect" the problem? I mean
>> > which patch in the series leads to those traps?
>> >
>> Oops sorry for not mentioning earlier, this is the offending patch
>> which leads to the issues seen on rz/five.
>
> Ok, so at least I found the following problem, but I don't see how
> that could fix your issue: can you give a try anyway? I keep looking
> into this, thanks
>
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index df2a0838c3a1..b5692bc6c76a 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -239,7 +239,7 @@ void flush_tlb_range(struct vm_area_struct *vma,
> unsigned long start,
>
>  void flush_tlb_kernel_range(unsigned long start, unsigned long end)
>  {
> -       __flush_tlb_range(NULL, start, end, PAGE_SIZE);
> +       __flush_tlb_range(NULL, start, end - start, PAGE_SIZE);
>  }
>
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE

Alex and I were talking a bit.  I'm OK just dropping the TLB flush 
series for this release, that way we can get to the bottom of what's 
wrong.

>
>>
>> Cheers,
>> Prabhakar