KVM: MMU: Optimize prefetch_page()

Instead of reading each pte individually, read 256 bytes worth of ptes and
batch process them.

Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 15 insertions, 13 deletions

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 934c7b619396..4d918220baeb 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -460,8 +460,9 @@ static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t vaddr)
 static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
                                  struct kvm_mmu_page *sp)
 {
-        int i, offset = 0, r = 0;
-        pt_element_t pt;
+        int i, j, offset, r;
+        pt_element_t pt[256 / sizeof(pt_element_t)];
+        gpa_t pte_gpa;
 
         if (sp->role.metaphysical
             || (PTTYPE == 32 && sp->role.level > PT_PAGE_TABLE_LEVEL)) {
@@ -469,19 +470,20 @@ static void FNAME(prefetch_page)(struct kvm_vcpu *vcpu,
                 return;
         }
 
-        if (PTTYPE == 32)
+        pte_gpa = gfn_to_gpa(sp->gfn);
+        if (PTTYPE == 32) {
                 offset = sp->role.quadrant << PT64_LEVEL_BITS;
+                pte_gpa += offset * sizeof(pt_element_t);
+        }
 
-        for (i = 0; i < PT64_ENT_PER_PAGE; ++i) {
-                gpa_t pte_gpa = gfn_to_gpa(sp->gfn);
-                pte_gpa += (i+offset) * sizeof(pt_element_t);
-
-                r = kvm_read_guest_atomic(vcpu->kvm, pte_gpa, &pt,
-                                          sizeof(pt_element_t));
-                if (r || is_present_pte(pt))
-                        sp->spt[i] = shadow_trap_nonpresent_pte;
-                else
-                        sp->spt[i] = shadow_notrap_nonpresent_pte;
+        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;
         }
 }