Re: [PATCH 4/7] kvm mmu: implement necessary data structures for second huge page accounting

Avi Kivity
2009-03-29T13:27:07Z

Joerg Roedel wrote:
> This patch adds the necessary data structures to take care of write
> protections in place within a second huge page sized page.
>
>
> +#ifdef KVM_PAGES_PER_LHPAGE
> + if (npages && !new.hpage_info) {
> + int hugepages = npages / KVM_PAGES_PER_LHPAGE;
> + if (npages % KVM_PAGES_PER_LHPAGE)
> + hugepages++;
> + if (base_gfn % KVM_PAGES_PER_LHPAGE)
> + hugepages++;
>

Consider a slot with base_gfn == 1 and npages == 1. This will have
hugepages == 2, which is wrong.

I think the right calculation is

((base_gfn + npages - 1) / N) - (base_gfn / N) + 1

i.e. index of last page, plus one so we can store it.

The small huge page calculation is off as well.

> +
> + new.hpage_info = vmalloc(hugepages * sizeof(*new.hpage_info));
> +
> + if (!new.hpage_info)
> + goto out_free;
> +
> + memset(new.hpage_info, 0, hugepages * sizeof(*new.hpage_info));
> +
> + if (base_gfn % KVM_PAGES_PER_LHPAGE)
> + new.hpage_info[0].write_count = 1;
> + if ((base_gfn+npages) % KVM_PAGES_PER_LHPAGE)
> + new.hpage_info[hugepages-1].write_count = 1;
> + }
> +#endif
> +
>

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