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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 Apr 7, 2019, at 2:23 AM, Thomas Gleixner <> wrote:
>> 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.

Fair enough. Although the patch I emailed in the other thread allows at least the entry code to survive on 64-bit at the cost of just a couple lines of code.

But the kernel does indeed seem to work fine without the change. Feel free to disregard that part :)
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