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

[Arnd Bergmann]

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.

        Arnd