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

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, Jun 30, 2016 at 5:24 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Thu, Jun 30, 2016 at 8:17 AM, Rafael J. Wysocki <rafael@kernel.org> wrote:
>> On Thu, Jun 30, 2016 at 5:05 PM, Borislav Petkov <bp@alien8.de> wrote:
>>> On Thu, Jun 30, 2016 at 03:17:20PM +0200, Rafael J. Wysocki wrote:
>>>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>>
>>>> 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. :-)

Thanks,
Rafael