2021-11-17 16:38:23

by Paolo Bonzini

Subject: [PATCH 3/4] KVM: SEV: cleanup locking for KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM

Encapsulate the handling of the migration_in_progress flag for both VMs in
two functions sev_lock_two_vms and sev_unlock_two_vms. It does not matter
if KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM locks the source struct kvm a bit
earlier, and this change 1) keeps the cleanup chain of labels smaller 2)
makes it possible for KVM_CAP_VM_COPY_ENC_CONTEXT_FROM to reuse the logic.

Cc: Peter Gonda <[email protected]>
Cc: Sean Christopherson <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
---
arch/x86/kvm/svm/sev.c | 50 ++++++++++++++++++++----------------------
1 file changed, 24 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 21ac0a5de4e0..f9256ba269e6 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1543,28 +1543,37 @@ static bool is_cmd_allowed_from_mirror(u32 cmd_id)
return false;
}

-static int sev_lock_for_migration(struct kvm *kvm)
+static int sev_lock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
{
- struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+ 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;

/*
- * Bail if this VM is already involved in a migration to avoid deadlock
- * between two VMs trying to migrate to/from each other.
+ * Bail if these VMs are already involved in a migration to avoid
+ * deadlock between two VMs trying to migrate to/from each other.
*/
- if (atomic_cmpxchg_acquire(&sev->migration_in_progress, 0, 1))
+ if (atomic_cmpxchg_acquire(&dst_sev->migration_in_progress, 0, 1))
return -EBUSY;

- mutex_lock(&kvm->lock);
+ if (atomic_cmpxchg_acquire(&src_sev->migration_in_progress, 0, 1)) {
+ atomic_set_release(&dst_sev->migration_in_progress, 0);
+ return -EBUSY;
+ }

+ mutex_lock(&dst_kvm->lock);
+ mutex_lock(&src_kvm->lock);
return 0;
}

-static void sev_unlock_after_migration(struct kvm *kvm)
+static void sev_unlock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
{
- struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+ 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;

- mutex_unlock(&kvm->lock);
- atomic_set_release(&sev->migration_in_progress, 0);
+ mutex_unlock(&dst_kvm->lock);
+ mutex_unlock(&src_kvm->lock);
+ atomic_set_release(&dst_sev->migration_in_progress, 0);
+ atomic_set_release(&src_sev->migration_in_progress, 0);
}


@@ -1666,15 +1675,6 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
bool charged = false;
int ret;

- ret = sev_lock_for_migration(kvm);
- if (ret)
- return ret;
-
- if (sev_guest(kvm)) {
- ret = -EINVAL;
- goto out_unlock;
- }
-
source_kvm_file = fget(source_fd);
if (!file_is_kvm(source_kvm_file)) {
ret = -EBADF;
@@ -1682,13 +1682,13 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
}

source_kvm = source_kvm_file->private_data;
- ret = sev_lock_for_migration(source_kvm);
+ ret = sev_lock_two_vms(kvm, source_kvm);
if (ret)
goto out_fput;

- if (!sev_guest(source_kvm)) {
+ if (sev_guest(kvm) || !sev_guest(source_kvm)) {
ret = -EINVAL;
- goto out_source;
+ goto out_unlock;
}

src_sev = &to_kvm_svm(source_kvm)->sev_info;
@@ -1728,13 +1728,11 @@ int svm_vm_migrate_from(struct kvm *kvm, unsigned int source_fd)
sev_misc_cg_uncharge(cg_cleanup_sev);
put_misc_cg(cg_cleanup_sev->misc_cg);
cg_cleanup_sev->misc_cg = NULL;
-out_source:
- sev_unlock_after_migration(source_kvm);
+out_unlock:
+ sev_unlock_two_vms(kvm, source_kvm);
out_fput:
if (source_kvm_file)
fput(source_kvm_file);
-out_unlock:
- sev_unlock_after_migration(kvm);
return ret;
}

--
2.27.0

2021-11-17 17:47:47

by Peter Gonda

Subject: Re: [PATCH 3/4] KVM: SEV: cleanup locking for KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM

On Wed, Nov 17, 2021 at 9:38 AM Paolo Bonzini <[email protected]> wrote:
>
> Encapsulate the handling of the migration_in_progress flag for both VMs in
> two functions sev_lock_two_vms and sev_unlock_two_vms. It does not matter
> if KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM locks the source struct kvm a bit
> earlier, and this change 1) keeps the cleanup chain of labels smaller 2)
> makes it possible for KVM_CAP_VM_COPY_ENC_CONTEXT_FROM to reuse the logic.
>
> Cc: Peter Gonda <[email protected]>
> Cc: Sean Christopherson <[email protected]>
> Signed-off-by: Paolo Bonzini <[email protected]>

Acked-by: Peter Gonda <[email protected]>

I like the cleanup thanks Paolo.