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>

1 files changed, 14 insertions, 7 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;