On Tue, Oct 05, 2010 at 09:36:59AM +0200, Avi Kivity wrote:
> 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.
It'll not be so advantageous for ksm because there should be read-faults
very rarely on that case.
Will post.
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