[PATCH v3 7/7] ARM: implement support for vmap'ed stacks

[Guillaume Tucker]

On 17/11/2021 11:13, Ard Biesheuvel wrote:
> On Wed, 17 Nov 2021 at 12:12, Tony Lindgren <tony at atomide.com> wrote:
>>
>> * Ard Biesheuvel <ardb at kernel.org> [211117 10:49]:
>>> On Wed, 17 Nov 2021 at 10:08, Ard Biesheuvel <ardb at kernel.org> wrote:
>>>>
>>>> On Wed, 17 Nov 2021 at 10:07, Arnd Bergmann <arnd at arndb.de> wrote:
>>>>>
>>>>> On Wed, Nov 17, 2021 at 10:03 AM Arnd Bergmann <arnd at arndb.de> wrote:
>>>>>>
>>>>>> On Wed, Nov 17, 2021 at 9:36 AM Tony Lindgren <tony at atomide.com> wrote:
>>>>>>> * Ard Biesheuvel <ardb at kernel.org> [211117 08:29]:
>>>>>>>>
>>>>>>>> Thanks Tony, that is very helpful. I have a Beaglebone white somewhere
>>>>>>>> so I'll try and reproduce it locally as well.
>>>>>>>
>>>>>>> I think with Beaglebone you may hit this only with suspend/resume if at
>>>>>>> all. On am335x cpuidle is not shutting down the CPU. And only some models
>>>>>>> will suspend to deeper idle states as it depends on the PMIC.
>>>>>>>
>>>>>>> If you have some test patch to try, just let me know.
>>>>>>
>>>>>> I looked at how the sleep code is called and found that cpu_suspend()/
>>>>>> __cpu_suspend() has interesting manipulation of the stack pointer to
>>>>>> call the platform specific function with a simple 1:1 page table,
>>>>>> I would expect the problem somewhere in there, haven't pinpointed
>>>>>> the exact line yet, but if any of that code tries to local the physical
>>>>>> address of the stack using virt_to_phys or its asm equivalent, this
>>>>>> fails for a vmap stack.
>>>>>
>>>>> and just after sending this I see
>>>>>
>>>>> void __cpu_suspend_save(u32 *ptr, u32 ptrsz, u32 sp, u32 *save_ptr)
>>>>> {
>>>>>         *save_ptr = virt_to_phys(ptr);
>>>>>
>>>>> 'ptr' is a pointer to the stack here. It might not be the only place that
>>>>> needs fixing, but this clearly has to do a page table walk like
>>>>> vmalloc_to_page() does to get to the correct physical address.
>>>>>
>>>>
>>>> I had just arrived at the same conclusion. I'll fix this up and drop
>>>> it in kernelci.
>>>
>>> Updated branch here:
>>> https://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git/commit/?h=arm-vmap-stacks-v4
>>
>> Great that branch boots for me!
>>
> 
> Thanks for testing!

Tested-by: "kernelci.org bot" <bot at kernelci.org>

https://staging.kernelci.org/test/plan/id/6194fd2f85155923f71760ce/

Guillaume