[PATCH v6 55/60] i386/tdx: Fetch and validate CPUID of TD guest

Xiaoyao Li
2024-11-05T06:40:17Z

Use KVM_TDX_GET_CPUID to get the CPUIDs that are managed and enfored
by TDX module for TD guest. Check QEMU's configuration against the
fetched data.

Print wanring message when 1. a feature is not supported but requested
by QEMU or 2. QEMU doesn't want to expose a feature while it is enforced
enabled.

- If cpu->enforced_cpuid is not set, prints the warning message of both
1) and 2) and tweak QEMU's configuration.

- If cpu->enforced_cpuid is set, quit if any case of 1) or 2).

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
target/i386/kvm/tdx.c | 81 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 81 insertions(+)

diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
index e7e0f073dfc9..9cb099e160e4 100644
--- a/target/i386/kvm/tdx.c
+++ b/target/i386/kvm/tdx.c
@@ -673,6 +673,86 @@ static uint32_t tdx_adjust_cpuid_features(X86ConfidentialGuest *cg,
return value;
}

+
+static void tdx_fetch_cpuid(CPUState *cpu, struct kvm_cpuid2 *fetch_cpuid)
+{
+ int r;
+
+ r = tdx_vcpu_ioctl(cpu, KVM_TDX_GET_CPUID, 0, fetch_cpuid);
+ if (r) {
+ error_report("KVM_TDX_GET_CPUID failed %s", strerror(-r));
+ exit(1);
+ }
+}
+
+static int tdx_check_features(X86ConfidentialGuest *cg, CPUState *cs)
+{
+ uint64_t actual, requested, unavailable, forced_on;
+ g_autofree struct kvm_cpuid2 *fetch_cpuid;
+ const char *forced_on_prefix = NULL;
+ const char *unav_prefix = NULL;
+ struct kvm_cpuid_entry2 *entry;
+ X86CPU *cpu = X86_CPU(cs);
+ CPUX86State *env = &cpu->env;
+ FeatureWordInfo *wi;
+ FeatureWord w;
+ bool mismatch = false;
+
+ fetch_cpuid = g_malloc0(sizeof(*fetch_cpuid) +
+ sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES);
+ tdx_fetch_cpuid(cs, fetch_cpuid);
+
+ if (cpu->check_cpuid || cpu->enforce_cpuid) {
+ unav_prefix = "TDX doesn't support requested feature";
+ forced_on_prefix = "TDX forcibly sets the feature";
+ }
+
+ for (w = 0; w < FEATURE_WORDS; w++) {
+ wi = &feature_word_info[w];
+ actual = 0;
+
+ switch (wi->type) {
+ case CPUID_FEATURE_WORD:
+ entry = cpuid_find_entry(fetch_cpuid, wi->cpuid.eax, wi->cpuid.ecx);
+ if (!entry) {
+ /*
+ * If KVM doesn't report it means it's totally configurable
+ * by QEMU
+ */
+ continue;
+ }
+
+ actual = cpuid_entry_get_reg(entry, wi->cpuid.reg);
+ break;
+ case MSR_FEATURE_WORD:
+ /*
+ * TODO:
+ * validate MSR features when KVM has interface report them.
+ */
+ continue;
+ }
+
+ requested = env->features[w];
+ unavailable = requested & ~actual;
+ mark_unavailable_features(cpu, w, unavailable, unav_prefix);
+ if (unavailable) {
+ mismatch = true;
+ }
+
+ forced_on = actual & ~requested;
+ mark_forced_on_features(cpu, w, forced_on, forced_on_prefix);
+ if (forced_on) {
+ mismatch = true;
+ }
+ }
+
+ if (cpu->enforce_cpuid && mismatch) {
+ return -1;
+ }
+
+ return 0;
+}
+
static int tdx_validate_attributes(TdxGuest *tdx, Error **errp)
{
if ((tdx->attributes & ~tdx_caps->supported_attrs)) {
@@ -1019,4 +1099,5 @@ static void tdx_guest_class_init(ObjectClass *oc, void *data)
x86_klass->cpu_instance_init = tdx_cpu_instance_init;
x86_klass->cpu_realizefn = tdx_cpu_realizefn;
x86_klass->adjust_cpuid_features = tdx_adjust_cpuid_features;
+ x86_klass->check_features = tdx_check_features;
}
--
2.34.1