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SubjectRe: [patch V2 03/29] x86/irq/64: Remove a hardcoded irq_stack_union access
On Fri, Apr 05, 2019 at 05:07:01PM +0200, Thomas Gleixner wrote:
> From: Andy Lutomirski <luto@kernel.org>
>
> stack_overflow_check() is using both irq_stack_ptr and irq_stack_union to
> find the IRQ stack. That's going to break when vmapped irq stacks are
> introduced.
>
> Change it to just use irq_stack_ptr.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>
> ---
> arch/x86/kernel/irq_64.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
>
> --- a/arch/x86/kernel/irq_64.c
> +++ b/arch/x86/kernel/irq_64.c
> @@ -55,9 +55,8 @@ static inline void stack_overflow_check(
> regs->sp <= curbase + THREAD_SIZE)
> return;
>
> - irq_stack_top = (u64)this_cpu_ptr(irq_stack_union.irq_stack) +
> - STACK_TOP_MARGIN;
> irq_stack_bottom = (u64)__this_cpu_read(irq_stack_ptr);
> + irq_stack_top = irq_stack_bottom - IRQ_STACK_SIZE + STACK_TOP_MARGIN;

Not introduced in this patch, but the names for top and bottom are flipped,
both for irq_stack and estack. STACK_TOP_MARGIN should also be
STACK_BOTTOM_MARGIN. The actual checks are functionally correct, but holy
hell does it make reading the code confusing, and the WARN prints backwards
information.

E.g.:

swapper/10 has overflown the kernel stack

cur:ffffc900000bc000,sp:ffff888277b03f78
irq stk top-bottom:ffff888277b00080-ffff888277b04000
exception stk top-bottom:fffffe00001b4080-fffffe00001b9000


Printing out top-bottom for "cur" would also probably be helpful.

Let me know if you'd like me to send a patch, or if you'll fold a change
into this series.


For this patch,

Reviewed-by: Sean Christopherson <sean.j.christopherson@intel.com>

> if (regs->sp >= irq_stack_top && regs->sp <= irq_stack_bottom)
> return;
>
>
>

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