Re: [PATCH 3/4] KVM: MMU: Make kvm_handle_hva() handle range of addresses

Takuya Yoshikawa
2012-06-19T13:46:48Z

On Mon, 18 Jun 2012 15:11:42 +0300
Avi Kivity <avi@redhat.com> wrote:

> Potential for improvement: don't do 512 iterations on same large page.
>
> Something like
>
> if ((gfn ^ prev_gfn) & mask(level))
> ret |= handler(...)
>
> with clever selection of the first prev_gfn so it always matches (~gfn
> maybe).

I thought up a better solution:

1. Separate rmap_pde from lpage_info->write_count and
make this a simple array. (I once tried this.)

2. Use gfn_to_index() and loop over rmap array:
...
/* intersection check */
start = max(start, memslot->userspace_addr);
end = min(end, memslot->userspace_addr +
(memslot->npages << PAGE_SHIFT));
if (start > end)
continue;

/* hva to gfn conversion */
gfn_start = hva_to_gfn_memslot(start);
gfn_end = hva_to_gfn_memslot(end);

/* main part */
for each level {
rmapp = __gfn_to_rmap(gfn_start, level, memslot);
for (idx = gfn_to_index(gfn_start, memslot->base_gfn, level);
idx < gfn_to_index(gfn_end, memslot->base_gfn, level); idx++) {
...
/* loop over rmap array */
ret |= handler(kvm, rmapp + idx, data);
}
}

Thanks,
Takuya