On Tue, May 17, 2022 at 04:20:31PM -0400, Peter Xu wrote:
> On Tue, May 17, 2022 at 07:05:24PM +0000, David Matlack wrote:
> > +uint64_t perf_test_nested_pages(int nr_vcpus)
> > +{
> > + /*
> > + * 513 page tables to identity-map the L2 with 1G pages, plus a few
> > + * pages per-vCPU for data structures such as the VMCS.
> > + */
> > + return 513 + 10 * nr_vcpus;
>
> Shouldn't that 513 magic value be related to vm->max_gfn instead (rather
> than assuming all hosts have 39 bits PA)?
>
> If my math is correct, it'll require 1GB here just for the l2->l1 pgtables
> on a 5-level host to run this test nested. So I had a feeling we'd better
> still consider >4 level hosts some day very soon.. No strong opinion, as
> long as this test is not run by default.
I had a feeling that when I said N level I actually meant N-1 level in all
above, since 39 bits are for 3 level not 4 level?..
Then it's ~512GB pgtables on 5 level? If so I do think we'd better have a
nicer way to do this identity mapping..
I don't think it's very hard - walk the mem regions in kvm_vm.regions
should work for us?
--
Peter Xu
