Re: [PATCH 05/23] m68k: allow pte_offset_map[_lock]() to fail

Geert Uytterhoeven
2023-05-10T07:14:30Z

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