Linux v4.12 introduced[1] emulation of MSR_PLATFORM_INFO and
MSR_MISC_FEATURES_ENABLES, and enabled the
MSR_PLATFORM_INFO_CPUID_FAULT bit unconditionally. This made
guests incorrectly believe the VM emulates
MSR_MISC_FEATURES_ENABLES properly (which is not true because
QEMU has no migration code to handle the MSR).
The KVM_CAP_MSR_PLATFORM_INFO capability was added[2] to Linux
v4.19 to address the issue. Use it to disable emulation of
MSR_PLATFORM_INFO and stop incorrectly exposing cpuid_fault to
guests.
References:
[1] commit db2336a80489 ("KVM: x86: virtualize cpuid faulting")
[2] commit 6fbbde9a1969 ("KVM: x86: Control guest reads of MSR_PLATFORM_INFO")
Reported-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
Signed-off-by: Eduardo Habkost <ehabkost@xxxxxxxxxx>
---
target/i386/kvm.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/target/i386/kvm.c b/target/i386/kvm.c
index 9af4542fb8..9629f25c90 100644
--- a/target/i386/kvm.c
+++ b/target/i386/kvm.c
@@ -1647,6 +1647,14 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
}
}
+ /*
+ * QEMU doesn't initialize MSR_PLATFORM_INFO yet, so disable the MSR
+ * unconditionally until support for the MSR is properly implemented
+ */
+ if (kvm_check_extension(s, KVM_CAP_MSR_PLATFORM_INFO)) {
+ kvm_vm_enable_cap(s, KVM_CAP_MSR_PLATFORM_INFO, 0);
+ }
+
return 0;
}
--
2.18.0.rc1.1.g3f1ff2140
