[PATCH] kvm: fix GFP_KERNEL allocation in atomic section in kvm_dev_ioctl_create_vcpu()

fix an GFP_KERNEL allocation in atomic section: kvm_dev_ioctl_create_vcpu()
called kvm_mmu_init(), which calls alloc_pages(), while holding the vcpu.

The fix is to set up the MMU state in two phases: kvm_mmu_create() and
kvm_mmu_setup().

(NOTE: free_vcpus does an kvm_mmu_destroy() call so there's no need for any
extra teardown branch on allocation/init failure here.)
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Avi Kivity <avi@qumranet.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/kvm/kvm.h

@@ -319,7 +319,8 @@ int kvm_init_arch(struct kvm_arch_ops *ops, struct module *module);
 void kvm_exit_arch(void);
 
 void kvm_mmu_destroy(struct kvm_vcpu *vcpu);
-int kvm_mmu_init(struct kvm_vcpu *vcpu);
+int kvm_mmu_create(struct kvm_vcpu *vcpu);
+int kvm_mmu_setup(struct kvm_vcpu *vcpu);
 
 int kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
 void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);

drivers/kvm/kvm_main.c

@@ -522,12 +522,14 @@ static int kvm_dev_ioctl_create_vcpu(struct kvm *kvm, int n)
 	if (r < 0)
 		goto out_free_vcpus;
 
-	kvm_arch_ops->vcpu_load(vcpu);
+	r = kvm_mmu_create(vcpu);
+	if (r < 0)
+		goto out_free_vcpus;
 
-	r = kvm_arch_ops->vcpu_setup(vcpu);
+	kvm_arch_ops->vcpu_load(vcpu);
+	r = kvm_mmu_setup(vcpu);
 	if (r >= 0)
-		r = kvm_mmu_init(vcpu);
-
+		r = kvm_arch_ops->vcpu_setup(vcpu);
 	vcpu_put(vcpu);
 
 	if (r < 0)

drivers/kvm/mmu.c

@@ -639,28 +639,22 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)
 	return -ENOMEM;
 }
 
-int kvm_mmu_init(struct kvm_vcpu *vcpu)
+int kvm_mmu_create(struct kvm_vcpu *vcpu)
 {
-	int r;
-
 	ASSERT(vcpu);
 	ASSERT(!VALID_PAGE(vcpu->mmu.root_hpa));
 	ASSERT(list_empty(&vcpu->free_pages));
 
-	r = alloc_mmu_pages(vcpu);
-	if (r)
-		goto out;
-
-	r = init_kvm_mmu(vcpu);
-	if (r)
-		goto out_free_pages;
+	return alloc_mmu_pages(vcpu);
+}
 
-	return 0;
+int kvm_mmu_setup(struct kvm_vcpu *vcpu)
+{
+	ASSERT(vcpu);
+	ASSERT(!VALID_PAGE(vcpu->mmu.root_hpa));
+	ASSERT(!list_empty(&vcpu->free_pages));
 
-out_free_pages:
-	free_mmu_pages(vcpu);
-out:
-	return r;
+	return init_kvm_mmu(vcpu);
 }
 
 void kvm_mmu_destroy(struct kvm_vcpu *vcpu)