On 07/11/2010 10:38 PM, Alex Williamson wrote:
What
about page attributes?
There are two cases:
- snoop capable iommu - can use write-backed RAM, but need to enable
snoop. BARs still need to respect page attributes.
- older mmu - need to respect guest memory type; probably cannot be done
without kvm.
If the guest maps a BAR or RAM using write-combine memory type, can we
reflect that? This may provide a considerable performance benefit.
Do we do anything about this today in kvm device assignment? Maybe it's
buried in the kernel side bits and I've missed it. I would expect that
WC mappings in the guest carry through to host virtual mappings, but
maybe we can only do that with kvm.
Yes, see arch/x86/kvm/mmu.c, set_spte() calling ->get_mt_mask().
Strangely, it's qualified with tdp. Perhaps because of all of the scary
errata regarding mismatching memory types for a page.
The processor side mappings are
independent of the iommu mappings since devices don't care about such
things. Thanks,
Yeah.
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