Re: [patch 3/4] KVM: MMU: reload request from GET_DIRTY_LOG path

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Jul 21, 2014 at 04:14:24PM +0300, Gleb Natapov wrote:
> On Wed, Jul 09, 2014 at 04:12:53PM -0300, mtosatti@redhat.com wrote:
> > Reload remote vcpus MMU from GET_DIRTY_LOG codepath, before
> > deleting a pinned spte.
> > 
> > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> > 
> > ---
> >  arch/x86/kvm/mmu.c |   29 +++++++++++++++++++++++------
> >  1 file changed, 23 insertions(+), 6 deletions(-)
> > 
> > Index: kvm.pinned-sptes/arch/x86/kvm/mmu.c
> > ===================================================================
> > --- kvm.pinned-sptes.orig/arch/x86/kvm/mmu.c	2014-07-09 11:23:59.290744490 -0300
> > +++ kvm.pinned-sptes/arch/x86/kvm/mmu.c	2014-07-09 11:24:58.449632435 -0300
> > @@ -1208,7 +1208,8 @@
> >   *
> >   * Return true if tlb need be flushed.
> >   */
> > -static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool pt_protect)
> > +static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool pt_protect,
> > +			       bool skip_pinned)
> >  {
> >  	u64 spte = *sptep;
> >  
> > @@ -1218,6 +1219,22 @@
> >  
> >  	rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
> >  
> > +	if (is_pinned_spte(spte)) {
> > +		/* keep pinned spte intact, mark page dirty again */
> > +		if (skip_pinned) {
> > +			struct kvm_mmu_page *sp;
> > +			gfn_t gfn;
> > +
> > +			sp = page_header(__pa(sptep));
> > +			gfn = kvm_mmu_page_get_gfn(sp, sptep - sp->spt);
> > +
> > +			mark_page_dirty(kvm, gfn);
> > +			return false;
> Why not mark all pinned gfns as dirty in kvm_vm_ioctl_get_dirty_log() while
> populating dirty_bitmap_buffer?

The pinned gfns are per-vcpu. Requires looping all vcpus (not
scalable).


> > +		} else
> > +			mmu_reload_pinned_vcpus(kvm);
> Can you explain why do you need this?

Because if skip_pinned = false, we want vcpus to exit (called
from enable dirty logging codepath).