Zachary Amsden wrote:
> I recently sent off a fix for lazy vmalloc faults which can happen
> under paravirt when lazy mode is enabled. Unfortunately, I jumped the
> gun a bit on fixing this. I neglected to notice that since the new
> call to flush the MMU update queue is called from the page fault
> handler, it can be pre-empted. Both VMI and Xen use per-cpu variables
> to track lazy mode state, as all previous calls to set, disable, or
> flush lazy mode happened from a non-preemptable state.
Hm. Doing any kind of lazy-state operation with preemption enabled is
fundamentally meaningless. How does it get into a preemptable state
with a lazy mode enabled now? If a sequence of code with preempt
disabled touches a missing vmalloc mapping, it gets a fault to fix up
the mapping, and the fault handler can end up preempting the thread?
That sounds like a larger bug than just paravirt lazy mode problems.
J
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