linux-kernel - Re: [PATCH 05/23] m68k: allow pte_offset_map[

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Message-ID: <CAMuHMdWb0SrEs=cDzKW1Ai2UywnnpZip4pk9mOkiVGivPpj8sg@mail.gmail.com>
Date:   Wed, 10 May 2023 09:13:50 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Greg Ungerer <gerg@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Helge Deller <deller@....de>,
        John David Anglin <dave.anglin@...l.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Alexandre Ghiti <alexghiti@...osinc.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "David S. Miller" <davem@...emloft.net>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 05/23] m68k: allow pte_offset_map[_lock]() to fail

Hi Hugh,

Thanks for your patch!

On Wed, May 10, 2023 at 6:48 AM Hugh Dickins <hughd@...gle.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@...gle.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@...ux-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