From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eduardo Habkost Subject: [PATCH 1/2] i386: kvm: Disable arch_capabilities if MSR can't be set Date: Fri, 25 Jan 2019 20:06:05 -0200 Message-ID: <20190125220606.4864-2-ehabkost@redhat.com> References: <20190125220606.4864-1-ehabkost@redhat.com> Cc: Eduardo Habkost , kvm@vger.kernel.org, =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , KarimAllah Ahmed , Marcelo Tosatti , Robert Hoo , Darren Kenny , Tao Xu , Paolo Bonzini , Konrad Rzeszutek Wilk , Jim Mattson , David Woodhouse , Richard Henderson To: qemu-devel@nongnu.org Return-path: In-Reply-To: <20190125220606.4864-1-ehabkost@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org KVM has two bugs in the handling of MSR_IA32_ARCH_CAPABILITIES: 1) Linux commit commit 1eaafe91a0df ("kvm: x86: IA32_ARCH_CAPABILITIES is always supported") makes GET_SUPPORTED_CPUID return arch_capabilities even if running on SVM. This makes "-cpu host,migratable=off" incorrectly expose arch_capabilities on CPUID on AMD hosts (where the MSR is not emulated by KVM). 2) KVM_GET_MSR_INDEX_LIST does not return MSR_IA32_ARCH_CAPABILITIES if the MSR is not supported by the host CPU. This makes QEMU not initialize the MSR properly at kvm_put_msrs() on those hosts. Work around both bugs on the QEMU side, by checking if the MSR was returned by KVM_GET_MSR_INDEX_LIST before returning the feature flag on kvm_arch_get_supported_cpuid(). This has the unfortunate side effect of making arch_capabilities unavailable on hosts without hardware support for the MSR until bug #2 is fixed on KVM, but I can't see another way to work around bug #1 without that side effect. Signed-off-by: Eduardo Habkost --- Cc: Konrad Rzeszutek Wilk Cc: Jim Mattson Cc: KarimAllah Ahmed Cc: David Woodhouse Cc: Darren Kenny --- target/i386/kvm.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/target/i386/kvm.c b/target/i386/kvm.c index 9af4542fb8..4fa3e3806a 100644 --- a/target/i386/kvm.c +++ b/target/i386/kvm.c @@ -389,6 +389,15 @@ uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function, if (host_tsx_blacklisted()) { ret &= ~(CPUID_7_0_EBX_RTM | CPUID_7_0_EBX_HLE); } + } else if (function == 7 && index == 0 && reg == R_EDX) { + /* + * Linux incorrectly v4.17-v4.20 return ARCH_CAPABILITIES on SVM. + * We can detect the bug by checking if MSR_IA32_ARCH_CAPABILITIES is + * returned by KVM_GET_MSR_INDEX_LIST. + */ + if (!has_msr_arch_capabs) { + ret &= ~CPUID_7_0_EDX_ARCH_CAPABILITIES; + } } else if (function == 0x80000001 && reg == R_ECX) { /* * It's safe to enable TOPOEXT even if it's not returned by -- 2.18.0.rc1.1.g3f1ff2140