[PATCH v2 hci-8.0/hci-8.1 5/6] i386: keep v-vmsave-vmload for nested AMD guests on vz types up to vz9.2.0 #VSTOR-152264

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

On Zen 4 client parts (family 19h models 0x18-0x1f and 0x60-0x7f) the
6.12 kernel clears virtualized VMSAVE/VMLOAD in init_amd_zen4(), which
some BIOSes trigger on reboot, and KVM stops offering v-vmsave-vmload.
A nested guest (svm=on) started before has it in its CPUID, and QEMU
filters it on such a host, so migration, restore and snapshot revert
fail.

Add x-v-vmsave-vmload-compat and turn it on in pc_vz_9_2_compat: an
AMD guest keeps a requested v-vmsave-vmload. This does not turn host
VLS back on: KVM keeps intercepting VMLOAD and VMSAVE of the nested
guest and emulates them (nested_vmcb_needs_vls_intercept()), which is
only slower.

Signed-off-by: Denis V. Lunev <den@openvz.org>
---
 hw/i386/pc.c      | 1 +
 target/i386/cpu.c | 7 +++++++
 target/i386/cpu.h | 1 +
 3 files changed, 9 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 91198e8996c..5b2b2de4064 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -552,6 +552,7 @@ GlobalProperty pc_vz_9_2_compat[] = {
     { TYPE_X86_CPU, "x-tsx-compat", "on" },
     { TYPE_X86_CPU, "x-spec-ctrl-compat", "on" },
     { TYPE_X86_CPU, "x-bus-lock-detect-compat", "on" },
+    { TYPE_X86_CPU, "x-v-vmsave-vmload-compat", "on" },
 };
 const size_t pc_vz_9_2_compat_len = G_N_ELEMENTS(pc_vz_9_2_compat);
 
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 84abaf1ae31..52d7ffcb9ac 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -9134,6 +9134,11 @@ static uint64_t x86_cpu_compat_kept_features(X86CPU *cpu, FeatureWord w)
             }
         }
         break;
+    case FEAT_SVM:
+        if (cpu->v_vmsave_vmload_compat && IS_AMD_CPU(env)) {
+            kept = CPUID_SVM_V_VMSAVE_VMLOAD;
+        }
+        break;
     default:
         break;
     }
@@ -10102,6 +10107,8 @@ static const Property x86_cpu_properties[] = {
     DEFINE_PROP_BOOL("x-spec-ctrl-compat", X86CPU, spec_ctrl_compat, false),
     DEFINE_PROP_BOOL("x-bus-lock-detect-compat", X86CPU,
                      bus_lock_detect_compat, false),
+    DEFINE_PROP_BOOL("x-v-vmsave-vmload-compat", X86CPU,
+                     v_vmsave_vmload_compat, false),
 };
 
 #ifndef CONFIG_USER_ONLY
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index b5e2d88d5d5..4f8bcbe600a 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -2339,6 +2339,7 @@ struct ArchCPU {
     bool tsx_compat;
     bool spec_ctrl_compat;
     bool bus_lock_detect_compat;
+    bool v_vmsave_vmload_compat;
 
     /* Number of physical address bits supported */
     uint32_t phys_bits;
-- 
2.53.0