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SubjectRe: 8b275b3754 ("x86/irq/64: Remap the IRQ stack with guard pages"): BUG: unable to handle kernel paging request at ffffb659000a1000
On Sat, 6 Apr 2019, Andy Lutomirski wrote:
> I haven't spotted the actual bug yet, but the faulting instruction is:
>
> 2a: 65 8b 35 09 ca 75 63 mov %gs:*0x6375ca09(%rip),%esi
> # 0x6375ca3a <-- trapping instruction
>
> This seems to be faulting just above the top of the stack (the thing
> in RSP), so I suspect that there is some path that is shoving the
> remapped value into GSBASE, which is wrong.
>
> Also, FWIW, there was some reason that I initialized all the virtual
> mappings for all possible CPUs early. I don't remember what it was,
> and it may not have been a good reason, but I put at least some
> nonzero amount of thought into it :)

There is absolutely no reason to have irq stacks before init_IRQ(). 32bit
uses at runtime allocated irq stacks for years.

If the CPU takes a device interrupt before that, then there are way more
things which explode than just the irqstack pointer being NULL.

Thanks,

tglx

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