Re: [PATCH v4] x86/power/64: Fix kernel text mapping corruption during image restoration

[Andy Lutomirski]

On Thu, Jun 30, 2016 at 8:29 AM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
> On Thu, Jun 30, 2016 at 5:24 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> On Thu, Jun 30, 2016 at 8:17 AM, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote:
>>> On Thu, Jun 30, 2016 at 5:05 PM, Borislav Petkov <bp@xxxxxxxxx> wrote:
>>>> On Thu, Jun 30, 2016 at 03:17:20PM +0200, Rafael J. Wysocki wrote:
>>>>> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>>>>>
>>>>> Logan Gunthorpe reports that hibernation stopped working reliably for
>>>>> him after commit ab76f7b4ab23 (x86/mm: Set NX on gap between __ex_table
>>>>> and rodata).
>>>>
>>>> ...
>>>>
>>>>> +static int relocate_restore_code(void)
>>>>> +{
>>>>> +     pgd_t *pgd;
>>>>> +     pud_t *pud;
>>>>> +
>>>>> +     relocated_restore_code = get_safe_page(GFP_ATOMIC);
>>>>> +     if (!relocated_restore_code)
>>>>> +             return -ENOMEM;
>>>>> +
>>>>> +     memcpy((void *)relocated_restore_code, &core_restore_code, PAGE_SIZE);
>>>>> +
>>>>> +     /* Make the page containing the relocated code executable */
>>>>> +     pgd = (pgd_t *)__va(read_cr3()) + pgd_index(relocated_restore_code);
>>>>> +     pud = pud_offset(pgd, relocated_restore_code);
>>>>> +     if (pud_large(*pud)) {
>>>>> +             set_pud(pud, __pud(pud_val(*pud) & ~_PAGE_NX));
>>>>> +     } else {
>>>>> +             pmd_t *pmd = pmd_offset(pud, relocated_restore_code);
>>>>> +
>>>>> +             if (pmd_large(*pmd)) {
>>>>> +                     set_pmd(pmd, __pmd(pmd_val(*pmd) & ~_PAGE_NX));
>>>>> +             } else {
>>>>> +                     pte_t *pte = pte_offset_kernel(pmd, relocated_restore_code);
>>>>> +
>>>>> +                     set_pte(pte, __pte(pte_val(*pte) & ~_PAGE_NX));
>>>>> +             }
>>>>> +     }
>>>>> +     flush_tlb_all();
>>>>
>>>> I know you want to flush TLBs but this causes the splat below on the
>>>> resume kernel.
>>>>
>>>> Most likely because:
>>>>
>>>> resume_target_kernel() does local_irq_disable() and then
>>>>
>>>> swsusp_arch_resume() -> relocate_restore_code() -> flush_tlb_all()
>>>>
>>>> and smp_call_function_many() doesn't like it when IRQs are disabled.
>>>
>>> Right.
>>>
>>> Can I invoke __flush_tlb_all() from here to flush the TLB on the local
>>> CPU?  That should be sufficient IMO.
>>
>> Yes, unless there's another CPU already up at the time, but that seems unlikely.
>
> They are all offline at that time.
>
> OK, let me do that then.
>
>> FWIW, the CPU can and will cache the NX bit and the CPU will *not*
>> refresh the TLB before sending a page fault.  You definitely need to
>> flush.
>
> OK
>
>>  I wonder if this is also why you're seeing a certain amount of
>> random corruption.
>
> Well, the corruption we saw was not really random.  I can give you all
> of the details if you're interested, maybe you'll be able to figure
> out what might be happening. :-)

Sure, or at least in abbreviated form.  No guarantee that I'll have
any clue, though.

--Andy