[Devel] [PATCH hci-8.0/hci-8.1 6/6] i386: keep SVM leaf features without svm on vz types up to vz9.2.0 #PSBM-144630

[Denis V. Lunev]

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

Since commit 730319aef0f ("i386: Mask SVM features if nested SVM is
disabled", QEMU 5.1) the features of CPUID leaf 0x8000000a are dropped
when svm is off. QEMU 2.12 on Vz7 kept them, and a Vz7 host-model
guest runs with svm=off,npt=on,nrip-save=on. Moving it to a newer QEMU
fails in libvirt (PSBM-144630):

  guest CPU doesn't match specification: missing features: npt,nrip-save

Add x-svm-features-compat and turn it on in pc_vz_9_2_compat: requested
SVM leaf features stay when svm is off, both against the dependency
on svm and against the host. The guest sees no difference, because
cpu_x86_cpuid() reports leaf 0x8000000a only with svm, in QEMU 2.12 as
now.

Signed-off-by: Denis V. Lunev <den at openvz.org>
---
 hw/i386/pc.c      |  1 +
 target/i386/cpu.c | 12 ++++++++++++
 target/i386/cpu.h |  1 +
 3 files changed, 14 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 5b2b2de4064..9b6b51bd5f7 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -553,6 +553,7 @@ GlobalProperty pc_vz_9_2_compat[] = {
     { 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" },
+    { TYPE_X86_CPU, "x-svm-features-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 52d7ffcb9ac..0ac6fdd19c7 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -8996,6 +8996,12 @@ void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
 
     for (i = 0; i < ARRAY_SIZE(feature_dependencies); i++) {
         FeatureDep *d = &feature_dependencies[i];
+
+        /* CPUID leaf 0x8000000a stays empty without svm anyway */
+        if (cpu->svm_features_compat && d->to.index == FEAT_SVM) {
+            continue;
+        }
+
         if (!(env->features[d->from.index] & d->from.mask)) {
             uint64_t unavailable_features = env->features[d->to.index] & d->to.mask;
 
@@ -9138,6 +9144,10 @@ static uint64_t x86_cpu_compat_kept_features(X86CPU *cpu, FeatureWord w)
         if (cpu->v_vmsave_vmload_compat && IS_AMD_CPU(env)) {
             kept = CPUID_SVM_V_VMSAVE_VMLOAD;
         }
+        if (cpu->svm_features_compat &&
+            !(env->features[FEAT_8000_0001_ECX] & CPUID_EXT3_SVM)) {
+            kept = ~0ULL;
+        }
         break;
     default:
         break;
@@ -10109,6 +10119,8 @@ static const Property x86_cpu_properties[] = {
                      bus_lock_detect_compat, false),
     DEFINE_PROP_BOOL("x-v-vmsave-vmload-compat", X86CPU,
                      v_vmsave_vmload_compat, false),
+    DEFINE_PROP_BOOL("x-svm-features-compat", X86CPU,
+                     svm_features_compat, false),
 };
 
 #ifndef CONFIG_USER_ONLY
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 4f8bcbe600a..97e38013e46 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -2340,6 +2340,7 @@ struct ArchCPU {
     bool spec_ctrl_compat;
     bool bus_lock_detect_compat;
     bool v_vmsave_vmload_compat;
+    bool svm_features_compat;
 
     /* Number of physical address bits supported */
     uint32_t phys_bits;
-- 
2.53.0