Re: [patch 3/3] KVM: move postcommit flush to x86, as mmio sptes are x86 specific

Marcelo Tosatti
2012-08-27T19:13:32Z

On Mon, Aug 27, 2012 at 11:41:08PM +0900, Takuya Yoshikawa wrote:
> On Fri, 24 Aug 2012 15:54:59 -0300
> Marcelo Tosatti <mtosatti@redhat.com> wrote:
>
> > Other arches do not need this.
> >
> > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> >
> > Index: kvm/arch/x86/kvm/x86.c
> > ===================================================================
> > --- kvm.orig/arch/x86/kvm/x86.c
> > +++ kvm/arch/x86/kvm/x86.c
> > @@ -6455,6 +6455,14 @@ void kvm_arch_commit_memory_region(struc
> > kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
> > kvm_mmu_slot_remove_write_access(kvm, mem->slot);
> > spin_unlock(&kvm->mmu_lock);
> > + /*
> > + * If the new memory slot is created, we need to clear all
> > + * mmio sptes.
> > + */
> > + if (old.npages == 0 && npages) {
> > + kvm_mmu_zap_all(kvm);
> > + kvm_reload_remote_mmus(kvm);
> > + }
> > }
>
> Any explanation why (old.base_gfn != new.base_gfn) case can be
> omitted?

(old.base_gfn != new.base_gfn) check covers the cases

1. old.base_gfn = 0, new.base_gfn = !0 (slot creation)

and

x != 0, y != 0, x != y.
2. old.base_gfn = x, new.base_gfn = y (gpa base change)

Patch 2 covers case 2, so its only necessary to cover case
1 here.

Makes sense?

> Takuya
>
> >
> > void kvm_arch_flush_shadow_all(struct kvm *kvm)
> > Index: kvm/virt/kvm/kvm_main.c
> > ===================================================================
> > --- kvm.orig/virt/kvm/kvm_main.c
> > +++ kvm/virt/kvm/kvm_main.c
> > @@ -849,13 +849,6 @@ int __kvm_set_memory_region(struct kvm *
> >
> > kvm_arch_commit_memory_region(kvm, mem, old, user_alloc);
> >
> > - /*
> > - * If the new memory slot is created, we need to clear all
> > - * mmio sptes.
> > - */
> > - if (npages && old.base_gfn != mem->guest_phys_addr >> PAGE_SHIFT)
> > - kvm_arch_flush_shadow_all(kvm);
> > -
> > kvm_free_physmem_slot(&old, &new);
> > kfree(old_memslots);