Avi Kivity wrote:
I'm suggesting
check irqcount
if (wasnt_in_irq)
rsp = irqstack
++irqcount
If the NMI happens before the increment, we'll switch the stack
unconditionally, and if the NMI happens after the increment, then we
won't switch the stack, but we're guaranteed to be on the irqstack
anyway. The window size is negative :)
Similarly, the exit path should be
oldstack_reg = oldstack;
--irqcount;
rsp = oldstack_register;
To guarantee that by the time we decrement irqcount, we don't need the
stack anymore.
On the other hand, checking %rsp allows us to drop irqcount completely,
so maybe it's better.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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