Re: [patch 2/4] KVM: MMU: allow pinning spte translations (TDP-only)

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Jul 17, 2014 at 08:18:03PM +0300, Nadav Amit wrote:
> Small question if I may regarding kvm_mmu_pin_pages:
> 
> On 7/9/14, 10:12 PM, mtosatti@redhat.com wrote:
> >+
> >+static int kvm_mmu_pin_pages(struct kvm_vcpu *vcpu)
> >+{
> >+	struct kvm_pinned_page_range *p;
> >+	int r = 1;
> >+
> >+	if (is_guest_mode(vcpu))
> >+		return r;
> >+
> >+	if (!vcpu->arch.mmu.direct_map)
> >+		return r;
> >+
> >+	ASSERT(VALID_PAGE(vcpu->arch.mmu.root_hpa));
> >+
> >+	list_for_each_entry(p, &vcpu->arch.pinned_mmu_pages, link) {
> >+		gfn_t gfn_offset;
> >+
> >+		for (gfn_offset = 0; gfn_offset < p->npages; gfn_offset++) {
> >+			gfn_t gfn = p->base_gfn + gfn_offset;
> >+			int r;
> >+			bool pinned = false;
> >+
> >+			r = vcpu->arch.mmu.page_fault(vcpu, gfn << PAGE_SHIFT,
> >+						     PFERR_WRITE_MASK, false,
> >+						     true, &pinned);
> 
> I understand that the current use-case is for pinning only few
> pages. Yet, wouldn't it be better (for performance) to check whether
> the gfn uses a large page and if so to skip forward, increasing
> gfn_offset to point to the next large page?

Sure, that can be a lazy optimization and performed when necessary?

(feel free to do it in advance if you're interested in doing it 
now).