KVM: Add memory slot versioning and use it to provide fast guest write interface

Keep track of memslots changes by keeping generation number in memslots
structure. Provide kvm_write_guest_cached() function that skips
gfn_to_hva() translation if memslots was not changed since previous
invocation.

Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 63 insertions, 12 deletions

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 75fd590c021..228f00f8796 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -687,6 +687,7 @@ skip_lpage:
                 memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
                 if (mem->slot >= slots->nmemslots)
                         slots->nmemslots = mem->slot + 1;
+                slots->generation++;
                 slots->memslots[mem->slot].flags |= KVM_MEMSLOT_INVALID;
 
                 old_memslots = kvm->memslots;
@@ -721,6 +722,7 @@ skip_lpage:
         memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
         if (mem->slot >= slots->nmemslots)
                 slots->nmemslots = mem->slot + 1;
+        slots->generation++;
 
         /* actual memory is freed via old in kvm_free_physmem_slot below */
         if (!npages) {
@@ -851,10 +853,10 @@ int kvm_is_error_hva(unsigned long addr)
 }
 EXPORT_SYMBOL_GPL(kvm_is_error_hva);
 
-struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
+static struct kvm_memory_slot *__gfn_to_memslot(struct kvm_memslots *slots,
+                                                gfn_t gfn)
 {
         int i;
-        struct kvm_memslots *slots = kvm_memslots(kvm);
 
         for (i = 0; i < slots->nmemslots; ++i) {
                 struct kvm_memory_slot *memslot = &slots->memslots[i];
@@ -865,6 +867,11 @@ struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
         }
         return NULL;
 }
+
+struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn)
+{
+        return __gfn_to_memslot(kvm_memslots(kvm), gfn);
+}
 EXPORT_SYMBOL_GPL(gfn_to_memslot);
 
 int kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
@@ -927,12 +934,9 @@ int memslot_id(struct kvm *kvm, gfn_t gfn)
         return memslot - slots->memslots;
 }
 
-static unsigned long gfn_to_hva_many(struct kvm *kvm, gfn_t gfn,
+static unsigned long gfn_to_hva_many(struct kvm_memory_slot *slot, gfn_t gfn,
                                      gfn_t *nr_pages)
 {
-        struct kvm_memory_slot *slot;
-
-        slot = gfn_to_memslot(kvm, gfn);
         if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
                 return bad_hva();
 
@@ -944,7 +948,7 @@ static unsigned long gfn_to_hva_many(struct kvm *kvm, gfn_t gfn,
 
 unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
 {
-        return gfn_to_hva_many(kvm, gfn, NULL);
+        return gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, NULL);
 }
 EXPORT_SYMBOL_GPL(gfn_to_hva);
 
@@ -1054,7 +1058,7 @@ int gfn_to_page_many_atomic(struct kvm *kvm, gfn_t gfn, struct page **pages,
         unsigned long addr;
         gfn_t entry;
 
-        addr = gfn_to_hva_many(kvm, gfn, &entry);
+        addr = gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, &entry);
         if (kvm_is_error_hva(addr))
                 return -1;
 
@@ -1238,6 +1242,47 @@ int kvm_write_guest(struct kvm *kvm, gpa_t gpa, const void *data,
         return 0;
 }
 
+int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
+                              gpa_t gpa)
+{
+        struct kvm_memslots *slots = kvm_memslots(kvm);
+        int offset = offset_in_page(gpa);
+        gfn_t gfn = gpa >> PAGE_SHIFT;
+
+        ghc->gpa = gpa;
+        ghc->generation = slots->generation;
+        ghc->memslot = __gfn_to_memslot(slots, gfn);
+        ghc->hva = gfn_to_hva_many(ghc->memslot, gfn, NULL);
+        if (!kvm_is_error_hva(ghc->hva))
+                ghc->hva += offset;
+        else
+                return -EFAULT;
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_gfn_to_hva_cache_init);
+
+int kvm_write_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
+                           void *data, unsigned long len)
+{
+        struct kvm_memslots *slots = kvm_memslots(kvm);
+        int r;
+
+        if (slots->generation != ghc->generation)
+                kvm_gfn_to_hva_cache_init(kvm, ghc, ghc->gpa);
+
+        if (kvm_is_error_hva(ghc->hva))
+                return -EFAULT;
+
+        r = copy_to_user((void __user *)ghc->hva, data, len);
+        if (r)
+                return -EFAULT;
+        mark_page_dirty_in_slot(kvm, ghc->memslot, ghc->gpa >> PAGE_SHIFT);
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(kvm_write_guest_cached);
+
 int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len)
 {
         return kvm_write_guest_page(kvm, gfn, empty_zero_page, offset, len);
@@ -1263,11 +1308,9 @@ int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len)
 }
 EXPORT_SYMBOL_GPL(kvm_clear_guest);
 
-void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
+void mark_page_dirty_in_slot(struct kvm *kvm, struct kvm_memory_slot *memslot,
+                             gfn_t gfn)
 {
-        struct kvm_memory_slot *memslot;
-
-        memslot = gfn_to_memslot(kvm, gfn);
         if (memslot && memslot->dirty_bitmap) {
                 unsigned long rel_gfn = gfn - memslot->base_gfn;
 
@@ -1275,6 +1318,14 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
         }
 }
 
+void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
+{
+        struct kvm_memory_slot *memslot;
+
+        memslot = gfn_to_memslot(kvm, gfn);
+        mark_page_dirty_in_slot(kvm, memslot, gfn);
+}
+
 /*
  * The vCPU has executed a HLT instruction with in-kernel mode enabled.
  */