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

Kefeng Wang
2021-06-02T11:25:50Z

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@huawei.com>
> 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
>