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Date: Mon, 22 Nov 2021 19:50:34 -0500
From: Paolo Bonzini <pbonzini@...hat.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: pgonda@...gle.com
Subject: [PATCH 10/12] KVM: SEV: Prohibit migration of a VM that has mirrors
VMs that mirror an encryption context rely on the owner to keep the
ASID allocated. Performing a KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM
would cause a dangling ASID:
1. copy context from A to B (gets ref to A)
2. move context from A to L (moves ASID from A to L)
3. close L (releases ASID from L, B still references it)
The right way to do the handoff instead is to create a fresh mirror VM
on the destination first:
1. copy context from A to B (gets ref to A)
[later] 2. close B (releases ref to A)
3. move context from A to L (moves ASID from A to L)
4. copy context from L to M
So, catch the situation by adding a count of how many VMs are
mirroring this one's encryption context.
Fixes: 0b020f5af092 ("KVM: SEV: Add support for SEV-ES intra host migration")
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
arch/x86/kvm/svm/sev.c | 22 ++++++++++-
arch/x86/kvm/svm/svm.h | 1 +
.../selftests/kvm/x86_64/sev_migrate_tests.c | 37 +++++++++++++++++++
3 files changed, 59 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 025d9731b66c..89a716290fac 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1696,6 +1696,16 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
}
src_sev = &to_kvm_svm(source_kvm)->sev_info;
+
+ /*
+ * VMs mirroring src's encryption context rely on it to keep the
+ * ASID allocated, but below we are clearing src_sev->asid.
+ */
+ if (src_sev->num_mirrored_vms) {
+ ret = -EBUSY;
+ goto out_unlock;
+ }
+
dst_sev->misc_cg = get_current_misc_cg();
cg_cleanup_sev = dst_sev;
if (dst_sev->misc_cg != src_sev->misc_cg) {
@@ -1987,6 +1997,7 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
*/
source_sev = &to_kvm_svm(source_kvm)->sev_info;
kvm_get_kvm(source_kvm);
+ source_sev->num_mirrored_vms++;
/* Set enc_context_owner and copy its encryption context over */
mirror_sev = &to_kvm_svm(kvm)->sev_info;
@@ -2019,12 +2030,21 @@ void sev_vm_destroy(struct kvm *kvm)
struct list_head *head = &sev->regions_list;
struct list_head *pos, *q;
+ WARN_ON(sev->num_mirrored_vms);
+
if (!sev_guest(kvm))
return;
/* If this is a mirror_kvm release the enc_context_owner and skip sev cleanup */
if (is_mirroring_enc_context(kvm)) {
- kvm_put_kvm(sev->enc_context_owner);
+ struct kvm *owner_kvm = sev->enc_context_owner;
+ struct kvm_sev_info *owner_sev = &to_kvm_svm(owner_kvm)->sev_info;
+
+ mutex_lock(&owner_kvm->lock);
+ if (!WARN_ON(!owner_sev->num_mirrored_vms))
+ owner_sev->num_mirrored_vms--;
+ mutex_unlock(&owner_kvm->lock);
+ kvm_put_kvm(owner_kvm);
return;
}
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 5faad3dc10e2..1c7306c370fa 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -79,6 +79,7 @@ struct kvm_sev_info {
struct list_head regions_list; /* List of registered regions */
u64 ap_jump_table; /* SEV-ES AP Jump Table address */
struct kvm *enc_context_owner; /* Owner of copied encryption context */
+ unsigned long num_mirrored_vms; /* Number of VMs sharing this ASID */
struct misc_cg *misc_cg; /* For misc cgroup accounting */
atomic_t migration_in_progress;
};
diff --git a/tools/testing/selftests/kvm/x86_64/sev_migrate_tests.c b/tools/testing/selftests/kvm/x86_64/sev_migrate_tests.c
index d265cea5de85..29b18d565cf4 100644
--- a/tools/testing/selftests/kvm/x86_64/sev_migrate_tests.c
+++ b/tools/testing/selftests/kvm/x86_64/sev_migrate_tests.c
@@ -294,6 +294,41 @@ static void test_sev_mirror_parameters(void)
kvm_vm_free(vm_no_vcpu);
}
+static void test_sev_move_copy(void)
+{
+ struct kvm_vm *dst_vm, *sev_vm, *mirror_vm, *dst_mirror_vm;
+ int ret;
+
+ sev_vm = sev_vm_create(/* es= */ false);
+ dst_vm = aux_vm_create(true);
+ mirror_vm = aux_vm_create(false);
+ dst_mirror_vm = aux_vm_create(false);
+
+ sev_mirror_create(mirror_vm->fd, sev_vm->fd);
+ ret = __sev_migrate_from(dst_vm->fd, sev_vm->fd);
+ TEST_ASSERT(ret == -1 && errno == EBUSY,
+ "Cannot migrate VM that has mirrors. ret %d, errno: %d\n", ret,
+ errno);
+
+ /* The mirror itself can be migrated. */
+ sev_migrate_from(dst_mirror_vm->fd, mirror_vm->fd);
+ ret = __sev_migrate_from(dst_vm->fd, sev_vm->fd);
+ TEST_ASSERT(ret == -1 && errno == EBUSY,
+ "Cannot migrate VM that has mirrors. ret %d, errno: %d\n", ret,
+ errno);
+
+ /*
+ * mirror_vm is not a mirror anymore, dst_mirror_vm is. Thus,
+ * the owner can be copied as soon as dst_mirror_vm is gone.
+ */
+ kvm_vm_free(dst_mirror_vm);
+ sev_migrate_from(dst_vm->fd, sev_vm->fd);
+
+ kvm_vm_free(mirror_vm);
+ kvm_vm_free(dst_vm);
+ kvm_vm_free(sev_vm);
+}
+
int main(int argc, char *argv[])
{
if (kvm_check_cap(KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM)) {
@@ -301,6 +336,8 @@ int main(int argc, char *argv[])
test_sev_migrate_from(/* es= */ true);
test_sev_migrate_locking();
test_sev_migrate_parameters();
+ if (kvm_check_cap(KVM_CAP_VM_COPY_ENC_CONTEXT_FROM))
+ test_sev_move_copy();
}
if (kvm_check_cap(KVM_CAP_VM_COPY_ENC_CONTEXT_FROM)) {
test_sev_mirror(/* es= */ false);
--
2.27.0
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