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authorJim Mattson <jmattson@google.com>2018-05-09 14:29:35 -0700
committerRadim Krčmář <rkrcmar@redhat.com>2018-05-24 18:38:34 +0200
commit1eaafe91a0df4157521b6417b3dd8430bf5f52f0 (patch)
treedad0dafe997f6d7f7ec60383002eeeefc1125db6 /arch
parentc4d2188206bafa177ea58e9a25b952baa0bf7712 (diff)
kvm: x86: IA32_ARCH_CAPABILITIES is always supported
If there is a possibility that a VM may migrate to a Skylake host, then the hypervisor should report IA32_ARCH_CAPABILITIES.RSBA[bit 2] as being set (future work, of course). This implies that CPUID.(EAX=7,ECX=0):EDX.ARCH_CAPABILITIES[bit 29] should be set. Therefore, kvm should report this CPUID bit as being supported whether or not the host supports it. Userspace is still free to clear the bit if it chooses. For more information on RSBA, see Intel's white paper, "Retpoline: A Branch Target Injection Mitigation" (Document Number 337131-001), currently available at https://bugzilla.kernel.org/show_bug.cgi?id=199511. Since the IA32_ARCH_CAPABILITIES MSR is emulated in kvm, there is no dependency on hardware support for this feature. Signed-off-by: Jim Mattson <jmattson@google.com> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Fixes: 28c1c9fabf48 ("KVM/VMX: Emulate MSR_IA32_ARCH_CAPABILITIES") Cc: stable@vger.kernel.org Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/cpuid.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 82055b90a8b3..beadfe6e6893 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -495,6 +495,11 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
entry->ecx &= ~F(PKU);
entry->edx &= kvm_cpuid_7_0_edx_x86_features;
cpuid_mask(&entry->edx, CPUID_7_EDX);
+ /*
+ * We emulate ARCH_CAPABILITIES in software even
+ * if the host doesn't support it.
+ */
+ entry->edx |= F(ARCH_CAPABILITIES);
} else {
entry->ebx = 0;
entry->ecx = 0;