KVM: use separate generations for each address space

This will make it easier to support multiple address spaces in
kvm_gfn_to_hva_cache_init.  Instead of having to check the address
space id, we can keep on checking just the generation number.

Reviewed-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e21bac7ed5d38b9dde695d61073457733e74621f..a83c186cefc160964d2a59c2bb6b3a2383bc4203 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -506,11 +506,6 @@ static struct kvm_memslots *kvm_alloc_memslots(void)
        if (!slots)
                return NULL;
 
-       /*
-        * Init kvm generation close to the maximum to easily test the
-        * code of handling generation number wrap-around.
-        */
-       slots->generation = -150;
        for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
                slots->id_to_index[i] = slots->memslots[i].id = i;
 
@@ -641,9 +636,16 @@ static struct kvm *kvm_create_vm(unsigned long type)
 
        r = -ENOMEM;
        for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
-               kvm->memslots[i] = kvm_alloc_memslots();
-               if (!kvm->memslots[i])
+               struct kvm_memslots *slots = kvm_alloc_memslots();
+               if (!slots)
                        goto out_err_no_srcu;
+               /*
+                * Generations must be different for each address space.
+                * Init kvm generation close to the maximum to easily test the
+                * code of handling generation number wrap-around.
+                */
+               slots->generation = i * 2 - 150;
+               rcu_assign_pointer(kvm->memslots[i], slots);
        }
 
        if (init_srcu_struct(&kvm->srcu))
@@ -870,8 +872,14 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm,
         * Increment the new memslot generation a second time. This prevents
         * vm exits that race with memslot updates from caching a memslot
         * generation that will (potentially) be valid forever.
+        *
+        * Generations must be unique even across address spaces.  We do not need
+        * a global counter for that, instead the generation space is evenly split
+        * across address spaces.  For example, with two address spaces, address
+        * space 0 will use generations 0, 4, 8, ... while * address space 1 will
+        * use generations 2, 6, 10, 14, ...
         */
-       slots->generation++;
+       slots->generation += KVM_ADDRESS_SPACE_NUM * 2 - 1;
 
        kvm_arch_memslots_updated(kvm, slots);