KVM: x86: Emulate MSR_IA32_ARCH_CAPABILITIES on AMD hosts

commit 0cf9135b upstream.

The CPUID flag ARCH_CAPABILITIES is unconditioinally exposed to host
userspace for all x86 hosts, i.e. KVM advertises ARCH_CAPABILITIES
regardless of hardware support under the pretense that KVM fully
emulates MSR_IA32_ARCH_CAPABILITIES.  Unfortunately, only VMX hosts
handle accesses to MSR_IA32_ARCH_CAPABILITIES (despite KVM_GET_MSRS
also reporting MSR_IA32_ARCH_CAPABILITIES for all hosts).

Move the MSR_IA32_ARCH_CAPABILITIES handling to common x86 code so
that it's emulated on AMD hosts.

Fixes: 1eaafe91

 ("kvm: x86: IA32_ARCH_CAPABILITIES is always supported")
Reported-by: Xiaoyao Li <xiaoyao.li@linux.intel.com>
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.16:
 - Keep using guest_cpuid_has_arch_capabilities() to check the CPUID
 - Keep using rdmsrl() to get the initial value of IA32_ARCH_CAPABILITIES
 - Adjust filenames, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>