On Thu, Jul 15, 2010 at 03:44:48PM +0800, Xiao Guangrong wrote:
>
>
> Marcelo Tosatti wrote:
>
> >> How about just track access bit for speculative path, we set page both accessed and
> >> dirty(if it's writable) only if the access bit is set?
> >
> > A useful thing to do would be to allow read-only mappings, in the fault
> > path (Lai sent a few patches in that direction sometime ago but there
> > was no follow up).
> >
> > So in the case of a read-only fault from the guest, you'd inform
> > get_user_pages() that read-only access is acceptable (so swapcache pages
> > can be mapped, or qemu can mprotect(PROT_READ) guest memory).
> >
>
> Yeah, it's a great work, i guess Lai will post the new version soon.
>
> And, even we do this, i think the page dirty track is still needed, right?
> Then, how about my new idea to track page dirty for speculative path, just
> as below draft patch does:
>
> @@ -687,10 +687,11 @@ static void drop_spte(struct kvm *kvm, u64 *sptep, u64 new_spte)
> if (!is_rmap_spte(old_spte))
> return;
> pfn = spte_to_pfn(old_spte);
> - if (old_spte & shadow_accessed_mask)
> + if (old_spte & shadow_accessed_mask) {
> kvm_set_pfn_accessed(pfn);
> - if (is_writable_pte(old_spte))
> - kvm_set_pfn_dirty(pfn);
> + if (is_writable_pte(old_spte))
> + kvm_set_pfn_dirty(pfn);
> + }
> rmap_remove(kvm, sptep);
> }
>
> @@ -1920,8 +1921,11 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
> * demand paging).
> */
> spte = shadow_base_present_pte | shadow_dirty_mask;
> - if (!speculative)
> + if (!speculative) {
> spte |= shadow_accessed_mask;
> + if (is_writable_pte(*sptep))
> + kvm_set_pfn_dirty(pfn);
> + }
> if (!dirty)
> pte_access &= ~ACC_WRITE_MASK;
> if (pte_access & ACC_EXEC_MASK)
>
> It uses access bit to track both page accessed and page dirty, and it's rather cheap...
Xiao,
I don't understand it. What are you trying to achieve?
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
