[PATCH v2 09/29] KVM: SEV: Explicitly initialize the per vCPU ASID on SEV VM migration

[Yosry Ahmed <yosry@kernel.org>]

Explicitly initialize svm->asid on the destination vCPUs as part of SEV
VM migration, before calling sev_init_vmcb() to make sure the per-vCPU
ASID is initialized before the VMCB. This is currently unnecessary as
sev_init_vmcb() initializes the per-vCPU ASID anyway, but will be needed
when the ASID initialization is moved to vCPU creation.

Add a helper function for the ASID migration as more changes will be
needed with incoming changes.

Note that svm->asid is left as-is on the source vCPUs, even though the
ASID now belongs to the destination VM. Clearing it would be a nice
hardening measure, but it is not as simple as clearing src_svm->asid, as
the source and destination VMs do not necessarily have the same number
of vCPUs (e.g. for non SEV-ES), so NULL-handling would be needed in a
couple of places. Leave it alone for now.

Signed-off-by: Yosry Ahmed <yosry@kernel.org>
---
 arch/x86/kvm/svm/sev.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 706a91db7b44a..0fbb72d57e6da 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2032,6 +2032,12 @@ static void sev_unlock_two_vms(struct kvm *dst_kvm, struct kvm *src_kvm)
 	atomic_set_release(&src_sev->migration_in_progress, 0);
 }
 
+static void sev_vcpu_migrate_asid(struct vcpu_svm *dst_svm,
+				  unsigned int asid)
+{
+	dst_svm->asid = asid;
+}
+
 static void sev_migrate_from(struct kvm *dst_kvm, struct kvm *src_kvm)
 {
 	struct kvm_sev_info *dst = to_kvm_sev_info(dst_kvm);
@@ -2096,6 +2102,7 @@ static void sev_migrate_from(struct kvm *dst_kvm, struct kvm *src_kvm)
 	kvm_for_each_vcpu(i, dst_vcpu, dst_kvm) {
 		dst_svm = to_svm(dst_vcpu);
 
+		sev_vcpu_migrate_asid(dst_svm, dst->asid);
 		sev_init_vmcb(dst_svm, false);
 
 		if (!dst->es_active)
-- 
2.56.0.360.g66cac248cb-goog