[lkml]   [2008]   [Dec]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: kvm vmload/vmsave vs

* Avi Kivity <> wrote:

> Ingo Molnar wrote:
>>> I think it's enough to switch %rsp before incrementing irqcount, no?
>> no - that would introduce a small race: if an exception (say an NMI or
>> MCE, or a debug trap) happens in that small window then the exception
>> context thinks that it's on the IRQ stack already, and would use the
>> task stack.
> 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.

agreed, something like this would work too. My suggestion, to eliminate
irqcount altogether and just check RSP against the known-irqstack-range,
could result in slightly smaller (and thus faster) code, but it's a
marginal difference at best.


 \ /
  Last update: 2008-12-25 19:21    [W:0.030 / U:0.364 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site