KVM: Allow browsing memslots with mmu_lock

This allows reading memslots with only the mmu_lock hold for mmu
notifiers that runs in atomic context and with mmu_lock held.

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

2 files changed, 30 insertions, 11 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9870ce422920..c7b01efe0646 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3974,16 +3974,23 @@ int kvm_arch_set_memory_region(struct kvm *kvm,
          */
         if (!user_alloc) {
                 if (npages && !old.rmap) {
+                        unsigned long userspace_addr;
+
                         down_write(&current->mm->mmap_sem);
-                        memslot->userspace_addr = do_mmap(NULL, 0,
-                                                     npages * PAGE_SIZE,
-                                                     PROT_READ | PROT_WRITE,
-                                                     MAP_SHARED | MAP_ANONYMOUS,
-                                                     0);
+                        userspace_addr = do_mmap(NULL, 0,
+                                                 npages * PAGE_SIZE,
+                                                 PROT_READ | PROT_WRITE,
+                                                 MAP_SHARED | MAP_ANONYMOUS,
+                                                 0);
                         up_write(&current->mm->mmap_sem);
 
-                        if (IS_ERR((void *)memslot->userspace_addr))
-                                return PTR_ERR((void *)memslot->userspace_addr);
+                        if (IS_ERR((void *)userspace_addr))
+                                return PTR_ERR((void *)userspace_addr);
+
+                        /* set userspace_addr atomically for kvm_hva_to_rmapp */
+                        spin_lock(&kvm->mmu_lock);
+                        memslot->userspace_addr = userspace_addr;
+                        spin_unlock(&kvm->mmu_lock);
                 } else {
                         if (!old.user_alloc && old.rmap) {
                                 int ret;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a845890b6800..3735212cd3f8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -375,7 +375,15 @@ int __kvm_set_memory_region(struct kvm *kvm,
                 memset(new.rmap, 0, npages * sizeof(*new.rmap));
 
                 new.user_alloc = user_alloc;
-                new.userspace_addr = mem->userspace_addr;
+                /*
+                 * hva_to_rmmap() serialzies with the mmu_lock and to be
+                 * safe it has to ignore memslots with !user_alloc &&
+                 * !userspace_addr.
+                 */
+                if (user_alloc)
+                        new.userspace_addr = mem->userspace_addr;
+                else
+                        new.userspace_addr = 0;
         }
         if (npages && !new.lpage_info) {
                 int largepages = npages / KVM_PAGES_PER_HPAGE;
@@ -408,17 +416,21 @@ int __kvm_set_memory_region(struct kvm *kvm,
         }
 #endif /* not defined CONFIG_S390 */
 
-        if (mem->slot >= kvm->nmemslots)
-                kvm->nmemslots = mem->slot + 1;
-
         if (!npages)
                 kvm_arch_flush_shadow(kvm);
 
+        spin_lock(&kvm->mmu_lock);
+        if (mem->slot >= kvm->nmemslots)
+                kvm->nmemslots = mem->slot + 1;
+
         *memslot = new;
+        spin_unlock(&kvm->mmu_lock);
 
         r = kvm_arch_set_memory_region(kvm, mem, old, user_alloc);
         if (r) {
+                spin_lock(&kvm->mmu_lock);
                 *memslot = old;
+                spin_unlock(&kvm->mmu_lock);
                 goto out_free;
         }