On 01/25/2011 04:55 PM, Michael S. Tsirkin wrote:
>
> We can't make it unbounded in the kernel, since a malicious user
> could start creating an infinite amount of memory slots, pinning
> unbounded kernel memory.
How about keeping the slots in userspace memory, access them with copy
from user?
Some of the data is validated by the kernel, so it needs a kernel copy.
Other fields are completely internal to the kernel.
> If we make the limit much larger, we should start to think about
> efficiency. Every mmio vmexit is currently a linear scan of the
> memory slot table, which is efficient at a small number of slots,
> but not at a large number. We could conceivably encode the "no
> slot" information into a bit in the not-present spte.
OK, but the slots that Alex here wants to use are presumably
mostly not resulting in a pagefault at all, right?
Can we split such guys out so they don't slow mmio lookup?
Maybe keep *these* in userspace memory.
The algorithm is:
page fault:
for each slot:
if addr in slot:
populate spte
return
# no slot matches
mmio
so we have to try out all slots before we find out none of them are needed.
--
error compiling committee.c: too many arguments to function
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