Re: KVM overflows the stack

Avi Kivity
2008-07-17T14:15:24Z

Dave Hansen wrote:
> On Wed, 2008-07-16 at 23:08 -0700, Roland Dreier wrote:
>
>> > Yes, things like kvm_lapic_state are way too big to be on the
>> stack.
>>
>> I had a quick look at the code, and my worry about dynamic allocation
>> would be that handling allocation failure seems like it might get
>> tricky. Eg for handling struct kvm_pv_mmu_op_buffer (which is 528 bytes
>> on the stack in kvm_pv_mmu_op()) can you deal with an mmu op failing?
>>
>
> Well, you *better* be able to deal with it. :)
>
> This code is also doing a *ton* of copy_to/from_user(). If userspace
> had one of its input buffers swapped out (or one of its output buffers
> not faulted in yet) and we're out of memory enough to be failing
> kmallocs() then we're sure as heck also going to failing the user
> copies.
>
> I think it's a non-issue.
>
>

Yes, it's designed to be restartable. Returning 0 should be fine.

We can reduce the buffer size to 256 though. I wouldn't want an
allocation in this hot path.

--
error compiling committee.c: too many arguments to function