Re: [PATCH v2 4/7] ARM: mm: print out correct page table entries

[Kefeng Wang]

On 2021/6/2 18:44, Russell King (Oracle) wrote:
> On Wed, Jun 02, 2021 at 03:02:43PM +0800, Kefeng Wang wrote:
> > Like commit 67ce16ec15ce ("arm64: mm: print out correct page table entries")
> > does, drop the struct mm_struct argument of show_pte(), print the tables
> > based on the faulting address.
> >
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> This can be misleading on 32-bit ARM.
>
> The effective page tables for each thread are the threads *own* page
> tables. There is no hardware magic for addresses above PAGE_OFFSET being
> directed to the init_mm page tables.
>
> So, when we hit a fault in kernel space, we need to be printing the
> currently in-use page tables associated with the running thread.
>
> Hence:
>
> >   /*
> > - * This is useful to dump out the page tables associated with
> > - * 'addr' in mm 'mm'.
> > + * Dump out the page tables associated with 'addr' in the currently active mm
> >    */
> > -void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
> > +void show_pte(const char *lvl, unsigned long addr)
> >   {
> >   	pgd_t *pgd;
> > -
> > -	if (!mm)
> > +	struct mm_struct *mm;
> > +
> > +	if (addr < TASK_SIZE) {
> > +		mm = current->active_mm;
> > +		if (mm == &init_mm) {
> > +			printk("%s[%08lx] user address but active_mm is swapper\n",
> > +				lvl, addr);
> > +			return;
> > +		}
> > +	} else {
> >   		mm = &init_mm;
> > +	}
> is incorrect here.
>
> It's completely fine for architectures where kernel accesses always go
> to the init_mm page tables, but for 32-bit ARM that is not the case.
OK, I will drop this one, thanks
>