linux-kernel - Re: [PATCH 3/4] KVM: MMU: Make kvm_handle

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Date:	Tue, 19 Jun 2012 22:46:48 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
	mtosatti@...hat.com, agraf@...e.de, paulus@...ba.org,
	aarcange@...hat.com, kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: MMU: Make kvm_handle_hva() handle range of
 addresses

On Mon, 18 Jun 2012 15:11:42 +0300
Avi Kivity <avi@...hat.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
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