KVM: MMU: large page support

Create large pages mappings if the guest PTE's are marked as such and
the underlying memory is hugetlbfs backed.  If the largepage contains
write-protected pages, a large pte is not used.

Gives a consistent 2% improvement for data copies on ram mounted
filesystem, without NPT/EPT.

Anthony measures a 4% improvement on 4-way kernbench, with NPT.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 24 insertions, 1 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index c41eb57ce29b..31db9b4d3016 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -212,9 +212,13 @@ static void kvm_free_physmem_slot(struct kvm_memory_slot *free,
         if (!dont || free->dirty_bitmap != dont->dirty_bitmap)
                 vfree(free->dirty_bitmap);
 
+        if (!dont || free->lpage_info != dont->lpage_info)
+                vfree(free->lpage_info);
+
         free->npages = 0;
         free->dirty_bitmap = NULL;
         free->rmap = NULL;
+        free->lpage_info = NULL;
 }
 
 void kvm_free_physmem(struct kvm *kvm)
@@ -324,6 +328,25 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 new.user_alloc = user_alloc;
                 new.userspace_addr = mem->userspace_addr;
         }
+        if (npages && !new.lpage_info) {
+                int largepages = npages / KVM_PAGES_PER_HPAGE;
+                if (npages % KVM_PAGES_PER_HPAGE)
+                        largepages++;
+                if (base_gfn % KVM_PAGES_PER_HPAGE)
+                        largepages++;
+
+                new.lpage_info = vmalloc(largepages * sizeof(*new.lpage_info));
+
+                if (!new.lpage_info)
+                        goto out_free;
+
+                memset(new.lpage_info, 0, largepages * sizeof(*new.lpage_info));
+
+                if (base_gfn % KVM_PAGES_PER_HPAGE)
+                        new.lpage_info[0].write_count = 1;
+                if ((base_gfn+npages) % KVM_PAGES_PER_HPAGE)
+                        new.lpage_info[largepages-1].write_count = 1;
+        }
 
         /* Allocate page dirty bitmap if needed */
         if ((new.flags & KVM_MEM_LOG_DIRTY_PAGES) && !new.dirty_bitmap) {
@@ -467,7 +490,7 @@ int kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
 }
 EXPORT_SYMBOL_GPL(kvm_is_visible_gfn);
 
-static unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
+unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
 {
         struct kvm_memory_slot *slot;