[PATCH] target/i386: check for availability of MSR_IA32_UCODE_REV as an emulated MSR

[Paolo Bonzini <pbonzini@redhat.com>]

Even though MSR_IA32_UCODE_REV has been available long before Linux 5.6,
which added it to the emulated MSR list, a bug caused the microcode
version to revert to 0x100000000 on INIT.  As a result, processors other
than the bootstrap processor would not see the host microcode revision;
some Windows version complain loudly about this and crash with a
fairly explicit MICROCODE REVISION MISMATCH error.

[If running 5.6 prereleases, the kernel fix "KVM: x86: do not reset
 microcode version on INIT or RESET" should also be applied.]

Reported-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/kvm.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 6ef291d580..69eb43d796 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -105,6 +105,7 @@ static bool has_msr_smi_count;
 static bool has_msr_arch_capabs;
 static bool has_msr_core_capabs;
 static bool has_msr_vmx_vmfunc;
+static bool has_msr_ucode_rev;
 
 static uint32_t has_architectural_pmu_version;
 static uint32_t num_architectural_pmu_gp_counters;
@@ -2056,6 +2057,9 @@ static int kvm_get_supported_msrs(KVMState *s)
             case MSR_IA32_VMX_VMFUNC:
                 has_msr_vmx_vmfunc = true;
                 break;
+            case MSR_IA32_UCODE_REV:
+                has_msr_ucode_rev = true;
+                break;
             }
         }
     }
@@ -2696,8 +2700,7 @@ static void kvm_init_msrs(X86CPU *cpu)
                           env->features[FEAT_CORE_CAPABILITY]);
     }
 
-    if (kvm_arch_get_supported_msr_feature(kvm_state,
-                                           MSR_IA32_UCODE_REV)) {
+    if (has_msr_ucode_rev) {
         kvm_msr_entry_add(cpu, MSR_IA32_UCODE_REV, cpu->ucode_rev);
     }
 
-- 
2.21.0