i386/sev/igvm: do not reset guest policy if IGVM does not set it

The guest policy is set either through command-line or through IGVM. If none of
the above applies, default guest policy applies. However, if IGVM does not set
the guest policy, currently the policy gets set to 0 regardless of whether it
was previously set to default value or command line. This change fixes this by
checking if IGVM indeed has set a policy value. If not, do not reset existing
value.

This avoids guest crashes such as the following during reset when the IGVM
has not explicitly set any guest policies:

qemu-system-x86_64: sev_snp_launch_start: SNP_LAUNCH_START ret=-22 fw_error=0 ''
qemu-system-x86_64: sev_common_kvm_init: failed to create encryption context
qemu-system-x86_64: unable to rebuild guest: Operation not permitted(-1)

Reported-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Ani Sinha <anisinha@redhat.com>
Message-ID: <20260310094450.35861-3-anisinha@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/target/i386/sev.c b/target/i386/sev.c
index 549e6241769b26585a4c58e5ca392aba731bdfe7..cddffe0da8dd0ced21771398ded4a9a836aaaa7e 100644 (file)
--- a/target/i386/sev.c
+++ b/target/i386/sev.c
@@ -2760,7 +2760,11 @@ static int cgs_set_guest_policy(ConfidentialGuestPolicyType policy_type,
                 id_auth->author_key[0] ? 1 : 0;
             finish->id_block_en = 1;
         }
-        sev_snp_guest->kvm_start_conf.policy = policy;
+
+        /* do not reset existing policy if policy was not set in IGVM  */
+        if (policy != 0) {
+            sev_snp_guest->kvm_start_conf.policy = policy;
+        }
     } else {
         SevGuestState *sev_guest = SEV_GUEST(MACHINE(qdev_get_machine())->cgs);
         /* Only the policy flags are supported for SEV and SEV-ES */
@@ -2769,7 +2773,11 @@ static int cgs_set_guest_policy(ConfidentialGuestPolicyType policy_type,
                              "but SEV-SNP is not enabled", __func__);
             return -1;
         }
-        sev_guest->policy = policy;
+
+        /* do not reset existing policy if policy was not set in IGVM  */
+        if (policy != 0) {
+            sev_guest->policy = policy;
+        }
     }
     return 0;
 }