[PATCH] kvm memslot read-locking with mmu_lock

[Andrea Arcangeli <andrea-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

This adds locking to the memslots so they can be looked up with only
the mmu_lock. Entries with memslot->userspace_addr have to be ignored
because they're not fully inserted yet.

Signed-off-by: Andrea Arcangeli <andrea-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8a90403..35a2ee0 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3219,14 +3249,20 @@ int kvm_arch_set_memory_region(struct kvm *kvm,
 	 */
 	if (!user_alloc) {
 		if (npages && !old.rmap) {
-			memslot->userspace_addr = do_mmap(NULL, 0,
-						     npages * PAGE_SIZE,
-						     PROT_READ | PROT_WRITE,
-						     MAP_SHARED | MAP_ANONYMOUS,
-						     0);
-
-			if (IS_ERR((void *)memslot->userspace_addr))
-				return PTR_ERR((void *)memslot->userspace_addr);
+			unsigned long userspace_addr;
+			
+			userspace_addr = do_mmap(NULL, 0,
+						 npages * PAGE_SIZE,
+						 PROT_READ | PROT_WRITE,
+						 MAP_SHARED | MAP_ANONYMOUS,
+						 0);
+			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 4295623..a67e38f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -298,7 +299,15 @@ 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;
 	}
 
 	/* Allocate page dirty bitmap if needed */
@@ -311,14 +320,18 @@ int __kvm_set_memory_region(struct kvm *kvm,
 		memset(new.dirty_bitmap, 0, dirty_bytes);
 	}
 
+	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;
 	}
 

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