Re: [PATCH v2 1/3] x86/entry/64: Refactor IRQ stacks and make them NMI-safe

[Andy Lutomirski]

On Mon, Aug 17, 2015 at 4:18 AM, Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
> On Sat, Jul 25, 2015 at 8:57 AM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
>> This will allow IRQ stacks to nest inside NMIs or similar entries
>> that can happen during IRQ stack setup or teardown.
>>
>> The Xen code here has a confusing comment.
>>
>> The new macros won't work correctly if they're invoked with IRQs on.
>> Add a check under CONFIG_DEBUG_ENTRY to detect that.
>>
>
>> +/*
>> + * Enters the IRQ stack if we're not already using it.  NMI-safe.  Clobbers
>> + * flags and puts old RSP into old_rsp, and leaves all other GPRs alone.
>> + * Requires kernel GSBASE.
>> + *
>> + * The invariant is that, if irq_count != 1, then the IRQ stack is in use.
>> + */
>
> I might be wrong, but shouldn't be this read as 'if irq_count != -1' ?
>

Indeed.  Will fix for the next version.

--Andy
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