Messages in this thread | | | From | Andy Lutomirski <> | Date | Fri, 24 Oct 2014 17:22:31 -0700 | Subject | vmalloced stacks on x86_64? |
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Is there any good reason not to use vmalloc for x86_64 stacks?
The tricky bits I've thought of are:
- On any context switch, we probably need to probe the new stack before switching to it. That way, if it's going to fault due to an out-of-sync pgd, we still have a stack available to handle the fault.
- Any time we change cr3, we may need to check that the pgd corresponding to rsp is there. If now, we need to sync it over.
- For simplicity, we probably want all stack ptes to be present all the time. This is fine; vmalloc already works that way.
- If we overrun the stack, we double-fault. This should be easy to detect: any double-fault where rsp is less than 20 bytes from the bottom of the stack is a failure to deliver a non-IST exception due to a stack overflow. The question is: what do we do if this happens? We could just panic (guaranteed to work). We could also try to recover by killing the offending task, but that might be a bit challenging, since we're in IST context. We could do something truly awful: increment RSP by a few hundred bytes, point RIP at do_exit, and return from the double fault.
Thoughts? This shouldn't be all that much code.
--Andy
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