[PATCH v3 03/10] target/i386: Hide ARCH_CAPABILITIES for Hygon

IA32_ARCH_CAPABILITIES is an Intel-defined MSR.  KVM can synthesize the
CPUID bit and read-only MSR for non-Intel guests, and QEMU already hides
that interface for AMD CPU models because Windows may not expect it on
AMD-compatible CPUs.

Hygon Dhyana uses the HygonGenuine vendor string, so it currently skips
that AMD filter.  If arch-capabilities=on is requested, QEMU can expose
CPUID.7.0.EDX[ARCH_CAPABILITIES] and the associated MSR feature word to
a Hygon guest.

That creates a vendor-inconsistent CPU ABI: the guest sees an
AMD-compatible vendor and cache/topology interface, but also sees an
Intel-specific architectural capabilities MSR.  Guests that choose CPU
mitigation or feature paths from the vendor can mis-handle that
combination; Windows is known to be sensitive to ARCH_CAPABILITIES on
AMD-compatible CPUs.

Apply the same ARCH_CAPABILITIES hiding rule to Hygon CPUs when the vendor
CPU ABI compat gate is enabled.  Keep arch_cap_always_on as the migration
escape hatch, and keep the old Hygon CPUID/MSR output for pc-11.1 and
older machine types via x-hygon-vendor-abi-fixes=false.

Signed-off-by: Tina Zhang <[email protected]>
Reviewed-by: Zhao Liu <[email protected]>
---
 target/i386/cpu.c | 33 ++++++++++++++++++++++++---------
 1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index c87f4684a3..8666f66df8 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -8209,6 +8209,8 @@ static uint8_t x86_cpu_get_host_avx10_version(void)
     return ebx & 0xff;
 }
 
+static bool x86_cpu_should_hide_arch_capabilities(const X86CPU *cpu);
+
 uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w)
 {
     FeatureWordInfo *wi = &feature_word_info[w];
@@ -8294,15 +8296,7 @@ uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w)
         break;
 
     case FEAT_7_0_EDX:
-        /*
-         * Windows does not like ARCH_CAPABILITIES on AMD machines at all.
-         * Do not show the fake ARCH_CAPABILITIES MSR that KVM sets up,
-         * except if needed for migration.
-         *
-         * When arch_cap_always_on is removed, this tweak can move to
-         * kvm_arch_get_supported_cpuid.
-         */
-        if (cpu && IS_AMD_CPU(&cpu->env) && !cpu->arch_cap_always_on) {
+        if (cpu && x86_cpu_should_hide_arch_capabilities(cpu)) {
             unavail = CPUID_7_0_EDX_ARCH_CAPABILITIES;
         }
         break;
@@ -8608,6 +8602,27 @@ uint32_t cpu_x86_virtual_addr_width(CPUX86State *env)
     }
 }
 
+/*
+ * Windows does not like ARCH_CAPABILITIES on AMD machines at all.
+ * Do not show the fake ARCH_CAPABILITIES MSR that KVM sets up,
+ * except if needed for migration.  Apply the same rule to Hygon CPUs when
+ * the corrected vendor CPU ABI is enabled.
+ *
+ * When arch_cap_always_on is removed, this tweak can move to
+ * kvm_arch_get_supported_cpuid.
+ */
+static bool x86_cpu_should_hide_arch_capabilities(const X86CPU *cpu)
+{
+    const CPUX86State *env = &cpu->env;
+
+    if (cpu->arch_cap_always_on) {
+        return false;
+    }
+
+    return IS_AMD_CPU(env) ||
+           (cpu->hygon_vendor_abi_fixes && IS_HYGON_CPU(env));
+}
+
 /*
  * CPUID leaves 2 and 4 describe Intel cache information.  AMD CPUs use
  * extended cache leaves instead, and Hygon Dhyana follows that AMD/Hygon
-- 
2.43.7