On 23/08/2013 23:57, Peter Grehan wrote:
I always wondered about virtualization environments which have pageable
guest memory - how does the guest kernel handle situations where it
really needs non-pageable memory? Does is simply not care because for
it the memory access looks just like it isn't paged but is simply very,
very slow?
Yes - from the guest's point of view, what it thinks is physical memory
appears wired.
What about time-sensitive situations (like the originally
mentioned PCI-passthrough)?
PCI passthru is a special case since the h/w requires that the target
of a DMA transfer is present - there is currently no way for the IOMMU
to generate the equivalent of page faults. So, for PCI passthru, all of
guest memory has to be wired host memory.
For time-sensitive situations, there's not a lot of options other than
forcing guest memory to be wired, since there isn't visibility into the
host without having o/s-specific tools that could communicate this
information to the hypervisor.
Ok, that is how I understood it also, but I thought that maybe there was
some way of telling which guest memory belongs to the kernel and only
wire those pages.
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