On Wed, 23 Oct 2019, Cyrill Gorcunov wrote:
> On Wed, Oct 23, 2019 at 03:21:05PM +0200, Thomas Gleixner wrote:
> > Errm. estack_pages is statically initialized and it's an array of:.
> >
> > struct estack_pages {
> > u32 offs;
> > u16 size;
> > u16 type;
> > };
> >
> > [0,2,4,5,6,8,10,12] are guard pages so 0 is not that crappy at all
>
> Wait, Thomas, I might be wrong, but per-cpu is initialized to the pointer,
> the memory for this estack_pages has not yet been allocated, no?
static const
struct estack_pages estack_pages[CEA_ESTACK_PAGES] ____cacheline_aligned = {
EPAGERANGE(DF),
EPAGERANGE(NMI),
EPAGERANGE(DB1),
EPAGERANGE(DB),
EPAGERANGE(MCE),
};
It's statically allocated. So it's available from the very beginning.
> The diff I made to fetch the values are
>
> diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
> index 753b8cfe8b8a..bf0d755b6079 100644
> --- a/arch/x86/kernel/dumpstack_64.c
> +++ b/arch/x86/kernel/dumpstack_64.c
> @@ -101,8 +101,18 @@ static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
>
> /* Calc page offset from start of exception stacks */
> k = (stk - begin) >> PAGE_SHIFT;
> +
> /* Lookup the page descriptor */
> ep = &estack_pages[k];
> +
> + printk("stk 0x%lx k %u begin 0x%lx end 0x%lx estack_pages 0x%lx ep 0x%lx\n",
> + stk, k, begin, end, (long)(void *)&estack_pages[0], (long)(void *)ep);
> +
> + for (k = 0; k < CEA_ESTACK_PAGES; k++) {
> + long v = *(long *)(void *)&estack_pages[k];
> + printk("estack_pages[%d] = 0x%lx\n", k, v);
And as I explained to you properly decoded the values _ARE_ correct and
make sense.
> + }
> +
> /* Guard page? */
> if (!ep->size)
> return false;
>
>
> >
> > e.g. 0x51000 00001000
> >
> > bit 0-31: 00001000 Offset 0x1000: 1 Page
> > bit 32-47: 1000 Size 0x1000: 1 Page
> > bit 48-63: 5 Type 5: STACK_TYPE_EXCEPTION + ESTACK_DF
> >
> > So, no. This is NOT the problem.
>
> I drop the left of your reply. True, I agreed with anything you said.
>
> You know I didn't manage to dive more into this problem yesterday
> but if time permits I'll continue today. It is easily triggering
> under kvm (the kernel I'm building is almost without modules so
> I simply upload bzImage into the guest). FWIW, the config I'm
> using is https://gist.github.com/cyrillos/7cd5d2510a99af8ea872f07ac6f9095b
That's helpful because I enabled kmemleak and the kernel comes up just fine.
Thanks,
tglx
