diff options
| author | Paolo Bonzini <pbonzini@redhat.com> | 2025-07-14 10:19:36 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2025-07-17 15:50:45 +0200 |
| commit | d3a24134e37d57abd3e7445842cda2717f49e96d (patch) | |
| tree | 395acbcad67be3d40e53c3a51e687779036c337e | |
| parent | f96b157ebb93f94cd56ebbc99bc20982b8fd86ef (diff) | |
| download | qemu-d3a24134e37d57abd3e7445842cda2717f49e96d.zip qemu-d3a24134e37d57abd3e7445842cda2717f49e96d.tar.gz qemu-d3a24134e37d57abd3e7445842cda2717f49e96d.tar.bz2 | |
target/i386: do not expose ARCH_CAPABILITIES on AMD CPU
KVM emulates the ARCH_CAPABILITIES on x86 for both Intel and AMD
cpus, although the IA32_ARCH_CAPABILITIES MSR is an Intel-specific
MSR and it makes no sense to emulate it on AMD.
As a consequence, VMs created on AMD with qemu -cpu host and using
KVM will advertise the ARCH_CAPABILITIES feature and provide the
IA32_ARCH_CAPABILITIES MSR. This can cause issues (like Windows BSOD)
as the guest OS might not expect this MSR to exist on such cpus (the
AMD documentation specifies that ARCH_CAPABILITIES feature and MSR
are not defined on the AMD architecture).
A fix was proposed in KVM code, however KVM maintainers don't want to
change this behavior that exists for 6+ years and suggest changes to be
done in QEMU instead. Therefore, hide the bit from "-cpu host":
migration of -cpu host guests is only possible between identical host
kernel and QEMU versions, therefore this is not a problematic breakage.
If a future AMD machine does include the MSR, that would re-expose the
Windows guest bug; but it would not be KVM/QEMU's problem at that
point, as we'd be following a genuine physical CPU impl.
Reported-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | target/i386/kvm/kvm.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index e8c8be0..369626f 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -503,8 +503,12 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function, * Linux v4.17-v4.20 incorrectly return ARCH_CAPABILITIES on SVM hosts. * We can detect the bug by checking if MSR_IA32_ARCH_CAPABILITIES is * returned by KVM_GET_MSR_INDEX_LIST. + * + * But also, because Windows does not like ARCH_CAPABILITIES on AMD + * mcahines at all, do not show the fake ARCH_CAPABILITIES MSR that + * KVM sets up. */ - if (!has_msr_arch_capabs) { + if (!has_msr_arch_capabs || !(edx & CPUID_7_0_EDX_ARCH_CAPABILITIES)) { ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES; } } else if (function == 7 && index == 1 && reg == R_EAX) { |