On 05/08/2012 04:27 AM, Marcelo Tosatti wrote:
> On Mon, May 07, 2012 at 10:25:34PM -0300, Marcelo Tosatti wrote:
> > On Thu, May 03, 2012 at 02:22:58PM +0300, Avi Kivity wrote:
> > > This patchset implements unlocked TLB flushing for KVM. An operation that
> > > generates stale TLB entries can mark the TLB as dirty instead of flushing
> > > immediately, and then flush after releasing mmu_lock but before returning
> > > to the guest or the caller. A few call sites are converted too.
> > >
> > > Note not all call sites are easily convertible; as an example, sync_page()
> > > must flush before reading the guest page table.
> >
> > Huh? Are you referring to:
> >
> > * Note:
> > * We should flush all tlbs if spte is dropped even though guest is
> > * responsible for it. Since if we don't,
> > * kvm_mmu_notifier_invalidate_page
> > * and kvm_mmu_notifier_invalidate_range_start detect the mapping page
> > * isn't
> > * used by guest then tlbs are not flushed, so guest is allowed to
> > * access the
> > * freed pages.
> > * And we increase kvm->tlbs_dirty to delay tlbs flush in this case.
> >
> > With an increased dirtied_count the flush can be performed
> > by kvm_mmu_notifier_invalidate_page.
>
> Which is what patch 1 does. Your comment regarding sync_page()
> above is what is outdated, unless i am missing something.
I wasn't referring to that. sync_page() (and page_fault()) must be sure
the guest page table is write-protected before reading gptes from it.
(page_fault() reads it before write protection, but verifies it afterwards:
/*
* Verify that the gpte in the page we've just write
* protected is still there.
*/
if (FNAME(gpte_changed)(vcpu, gw, it.level - 1))
goto out_gpte_changed;
so we must kvm_cond_flush_remote_tlbs() before calling gpte_changed().
--
error compiling committee.c: too many arguments to function
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