On 02/03/2018 22:42, Radim Krčmář wrote: > Ok, sounds good. I've deferred it to rc5 as I think we'll want to use > this to replace the auto setting: I would not bet that it is going to > be safe to expose future bits, so having the userspace always sanitize > the capabilities would be safer (and more in line with what we do with > other MSRs). i.e. this patch would also > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > index 051dab74e4e9..86ea4a83af1f 100644 > --- a/arch/x86/kvm/vmx.c > +++ b/arch/x86/kvm/vmx.c > @@ -5740,9 +5740,6 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx) > ++vmx->nmsrs; > } > > - if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES)) > - rdmsrl(MSR_IA32_ARCH_CAPABILITIES, vmx->arch_capabilities); > - > vm_exit_controls_init(vmx, vmcs_config.vmexit_ctrl); > > /* 22.2.1, 20.8.1 */ I don't know. There are good reasons for both behaviors, and especially the following two for _not_ removing the rdmsr: 1) so far you could just pass the result of KVM_GET_SUPPORTED_CPUID to KVM_SET_CPUID2, and expect the result to be "as close as possible to the host"; 2) having different behavior for VMX and ARCH_CAPABILITIES MSRs would be confusing. I think I'm leaning more towards the following direction: whitelist ARCH_CAPABILITIES, like we do for the AMD LFENCE MSR already, and default the AMD LFENCE MSR to the host value. Thanks, Paolo
