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Subject[PATCH 4/4] KVM: SEV: Do COPY_ENC_CONTEXT_FROM with both VMs locked
Date
Now that we have a facility to lock two VMs with deadlock
protection, use it for the creation of mirror VMs as well. One of
COPY_ENC_CONTEXT_FROM(dst, src) and COPY_ENC_CONTEXT_FROM(src, dst)
would always fail, so the combination is nonsensical and it is okay to
return -EBUSY if it is attempted.

This sidesteps the question of what happens if a VM is
MOVE_ENC_CONTEXT_FROM'd at the same time as it is
COPY_ENC_CONTEXT_FROM'd: the locking prevents that from
happening.

Cc: Peter Gonda <pgonda@google.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/svm/sev.c | 68 ++++++++++++++++--------------------------
1 file changed, 26 insertions(+), 42 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index f9256ba269e6..47d54df7675c 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1548,6 +1548,9 @@ static int sev_lock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
struct kvm_sev_info *dst_sev = &to_kvm_svm(dst_kvm)->sev_info;
struct kvm_sev_info *src_sev = &to_kvm_svm(src_kvm)->sev_info;

+ if (dst_kvm == src_kvm)
+ return -EINVAL;
+
/*
* Bail if these VMs are already involved in a migration to avoid
* deadlock between two VMs trying to migrate to/from each other.
@@ -1951,76 +1954,57 @@ int svm_vm_copy_asid_from(struct kvm *kvm, unsigned int source_fd)
{
struct file *source_kvm_file;
struct kvm *source_kvm;
- struct kvm_sev_info source_sev, *mirror_sev;
+ struct kvm_sev_info *source_sev, *mirror_sev;
int ret;

source_kvm_file = fget(source_fd);
if (!file_is_kvm(source_kvm_file)) {
ret = -EBADF;
- goto e_source_put;
+ goto e_source_fput;
}

source_kvm = source_kvm_file->private_data;
- mutex_lock(&source_kvm->lock);
-
- if (!sev_guest(source_kvm)) {
- ret = -EINVAL;
- goto e_source_unlock;
- }
+ ret = sev_lock_two_vms(kvm, source_kvm);
+ if (ret)
+ goto e_source_fput;

- /* Mirrors of mirrors should work, but let's not get silly */
- if (is_mirroring_enc_context(source_kvm) || source_kvm == kvm) {
+ /*
+ * Mirrors of mirrors should work, but let's not get silly. Also
+ * disallow out-of-band SEV/SEV-ES init if the target is already an
+ * SEV guest, or if vCPUs have been created. KVM relies on vCPUs being
+ * created after SEV/SEV-ES initialization, e.g. to init intercepts.
+ */
+ if (sev_guest(kvm) || !sev_guest(source_kvm) ||
+ is_mirroring_enc_context(source_kvm) || kvm->created_vcpus) {
ret = -EINVAL;
- goto e_source_unlock;
+ goto e_unlock;
}

- memcpy(&source_sev, &to_kvm_svm(source_kvm)->sev_info,
- sizeof(source_sev));
-
/*
* The mirror kvm holds an enc_context_owner ref so its asid can't
* disappear until we're done with it
*/
+ source_sev = &to_kvm_svm(source_kvm)->sev_info;
kvm_get_kvm(source_kvm);

- fput(source_kvm_file);
- mutex_unlock(&source_kvm->lock);
- mutex_lock(&kvm->lock);
-
- /*
- * Disallow out-of-band SEV/SEV-ES init if the target is already an
- * SEV guest, or if vCPUs have been created. KVM relies on vCPUs being
- * created after SEV/SEV-ES initialization, e.g. to init intercepts.
- */
- if (sev_guest(kvm) || kvm->created_vcpus) {
- ret = -EINVAL;
- goto e_mirror_unlock;
- }
-
/* Set enc_context_owner and copy its encryption context over */
mirror_sev = &to_kvm_svm(kvm)->sev_info;
mirror_sev->enc_context_owner = source_kvm;
mirror_sev->active = true;
- mirror_sev->asid = source_sev.asid;
- mirror_sev->fd = source_sev.fd;
- mirror_sev->es_active = source_sev.es_active;
- mirror_sev->handle = source_sev.handle;
+ mirror_sev->asid = source_sev->asid;
+ mirror_sev->fd = source_sev->fd;
+ mirror_sev->es_active = source_sev->es_active;
+ mirror_sev->handle = source_sev->handle;
+ ret = 0;
/*
* Do not copy ap_jump_table. Since the mirror does not share the same
* KVM contexts as the original, and they may have different
* memory-views.
*/

- mutex_unlock(&kvm->lock);
- return 0;
-
-e_mirror_unlock:
- mutex_unlock(&kvm->lock);
- kvm_put_kvm(source_kvm);
- return ret;
-e_source_unlock:
- mutex_unlock(&source_kvm->lock);
-e_source_put:
+e_unlock:
+ sev_unlock_two_vms(kvm, source_kvm);
+e_source_fput:
if (source_kvm_file)
fput(source_kvm_file);
return ret;
--
2.27.0
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