[patch 04/13] KVM: MMU: switch prefetch_page to gfn_to_page_atomic

[Marcelo Tosatti <mtosatti@redhat.com>]

[-- Attachment #1: prefetch-page-use-gfn-to-page-atomic --]
[-- Type: text/plain, Size: 1796 bytes --]

Close to 50% improvement for prefetch_page.

Index: kvm/arch/x86/kvm/paging_tmpl.h
===================================================================
--- kvm.orig/arch/x86/kvm/paging_tmpl.h
+++ kvm/arch/x86/kvm/paging_tmpl.h
@@ -477,9 +477,10 @@ static gpa_t FNAME(gva_to_gpa)(struct kv
 static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
 				 struct kvm_mmu_page *sp)
 {
-	int i, j, offset, r;
-	pt_element_t pt[256 / sizeof(pt_element_t)];
-	gpa_t pte_gpa;
+	int i;
+	struct page *page;
+	pt_element_t *pt;
+	void *gpte_kaddr;
 
 	if (sp->role.metaphysical
 	    || (PTTYPE == 32 && sp->role.level > PT_PAGE_TABLE_LEVEL)) {
@@ -487,21 +488,26 @@ static void FNAME(prefetch_page)(struct 
 		return;
 	}
 
-	pte_gpa = gfn_to_gpa(sp->gfn);
-	if (PTTYPE == 32) {
-		offset = sp->role.quadrant << PT64_LEVEL_BITS;
-		pte_gpa += offset * sizeof(pt_element_t);
+	page = gfn_to_page_atomic(vcpu->kvm, sp->gfn);
+	if (is_error_page(page)) {
+		nonpaging_prefetch_page(vcpu, sp);
+		kvm_release_page_clean(page);
+		return;
 	}
+	gpte_kaddr = pt = kmap_atomic(page, KM_USER0);
+
+	if (PTTYPE == 32)
+		pt += sp->role.quadrant << PT64_LEVEL_BITS;
 
-	for (i = 0; i < PT64_ENT_PER_PAGE; i += ARRAY_SIZE(pt)) {
-		r = kvm_read_guest_atomic(vcpu->kvm, pte_gpa, pt, sizeof pt);
-		pte_gpa += ARRAY_SIZE(pt) * sizeof(pt_element_t);
-		for (j = 0; j < ARRAY_SIZE(pt); ++j)
-			if (r || is_present_pte(pt[j]))
-				sp->spt[i+j] = shadow_trap_nonpresent_pte;
-			else
-				sp->spt[i+j] = shadow_notrap_nonpresent_pte;
+	for (i = 0; i < PT64_ENT_PER_PAGE; i++) {
+		if (is_present_pte(*pt))
+			sp->spt[i] = shadow_trap_nonpresent_pte;
+		else
+			sp->spt[i] = shadow_notrap_nonpresent_pte;
+		pt++;
 	}
+	kunmap_atomic(gpte_kaddr, KM_USER0);
+	kvm_release_page_clean(page);
 }
 
 #undef pt_element_t

--