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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 10 May 2023 09:13:50 +0200
Message-ID: <CAMuHMdWb0SrEs=cDzKW1Ai2UywnnpZip4pk9mOkiVGivPpj8sg@mail.gmail.com>
Subject: Re: [PATCH 05/23] m68k: allow pte_offset_map[_lock]() to fail
To:     Hugh Dickins <hughd@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        David Hildenbrand <david@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
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Hi Hugh,

Thanks for your patch!

On Wed, May 10, 2023 at 6:48 AM Hugh Dickins <hughd@google.com> wrote:
> In rare transient cases, not yet made possible, pte_offset_map() and
> pte_offset_map_lock() may not find a page table: handle appropriately.
>
> Restructure cf_tlb_miss() with a pte_unmap() (previously omitted)
> at label out, followed by one local_irq_restore() for all.

That's a bug fix, which should be a separate patch?

>
> Signed-off-by: Hugh Dickins <hughd@google.com>


> --- a/arch/m68k/include/asm/mmu_context.h
> +++ b/arch/m68k/include/asm/mmu_context.h
> @@ -99,7 +99,7 @@ static inline void load_ksp_mmu(struct task_struct *task)
>         p4d_t *p4d;
>         pud_t *pud;
>         pmd_t *pmd;
> -       pte_t *pte;
> +       pte_t *pte = NULL;
>         unsigned long mmuar;
>
>         local_irq_save(flags);
> @@ -139,7 +139,7 @@ static inline void load_ksp_mmu(struct task_struct *task)
>
>         pte = (mmuar >= PAGE_OFFSET) ? pte_offset_kernel(pmd, mmuar)
>                                      : pte_offset_map(pmd, mmuar);
> -       if (pte_none(*pte) || !pte_present(*pte))
> +       if (!pte || pte_none(*pte) || !pte_present(*pte))
>                 goto bug;

If the absence of a pte is to become a non-abnormal case, it should
probably jump to "end" instead, to avoid spamming the kernel log.

>
>         set_pte(pte, pte_mkyoung(*pte));
> @@ -161,6 +161,8 @@ static inline void load_ksp_mmu(struct task_struct *task)
>  bug:
>         pr_info("ksp load failed: mm=0x%p ksp=0x08%lx\n", mm, mmuar);
>  end:
> +       if (pte && mmuar < PAGE_OFFSET)
> +               pte_unmap(pte);

Is this also a bugfix, not mentioned in the patch description?

>         local_irq_restore(flags);
>  }
>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds