From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: unit tests and get_user_pages_ptes_fast()
Date: Tue, 05 Oct 2010 09:36:59 +0200
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References: <4CA99FE0.7070709@redhat.com> <20101004134052.GQ26357@random.random> <20101004235953.GA1474@amt.cnet>
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Cc: Andrea Arcangeli <aarcange@redhat.com>,
	KVM list <kvm@vger.kernel.org>
To: Marcelo Tosatti <mtosatti@redhat.com>
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  On 10/05/2010 01:59 AM, Marcelo Tosatti wrote:
> Yep, the drawback is the unnecessary write fault. What i have here is:
>
> --- kvm.orig/virt/kvm/kvm_main.c
> +++ kvm/virt/kvm/kvm_main.c
> @@ -827,7 +827,7 @@ unsigned long gfn_to_hva(struct kvm *kvm
>   }
>   EXPORT_SYMBOL_GPL(gfn_to_hva);
>
> -pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
> +pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn, int *writable)
>   {
>          struct page *page[1];
>          unsigned long addr;
> @@ -842,8 +842,16 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t
>                  return page_to_pfn(bad_page);
>          }
>
> +       *writable = 1;
>          npages = get_user_pages_fast(addr, 1, 1, page);
>
> +       /* attempt to map read-only */
> +       if (unlikely(npages != 1)) {
> +               npages = get_user_pages_fast(addr, 1, 0, page);
> +               if (npages == 1)
> +                       *writable = 0;
> +       }
> +
>          if (unlikely(npages != 1)) {
>                  struct vm_area_struct *vma;
>
> Can rebase and resend, if you'd like.
>

That will work for me but not for ksm.  I guess it's good to get things 
going, so please to post it.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.