Re: [PATCH 06/26] KVM: x86: Move MSR_IA32_BNDCFGS existence checks into vendor code

Vitaly Kuznetsov
2020-02-05T14:53:56Z

Sean Christopherson <sean.j.christopherson@intel.com> writes:

> Move the MSR_IA32_BNDCFGS existence check into vendor code by way of
> ->has_virtualized_msr(). AMD does not support MPX, and given that Intel
> is in the process of removing MPX, it's extremely unlikely AMD will ever
> support MPX.
>
> Note, invoking ->has_virtualized_msr() requires an extra retpoline, but
> kvm_init_msr_list() is not a hot path. As alluded to above, the
> motivation is to quarantine MPX as much as possible.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/svm.c | 2 ++
> arch/x86/kvm/vmx/vmx.c | 2 ++
> arch/x86/kvm/x86.c | 4 ----
> 3 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 4c8427f57b71..504118c49f46 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5990,6 +5990,8 @@ static bool svm_has_virtualized_msr(u32 index)
> switch (index) {
> case MSR_TSC_AUX:
> return boot_cpu_has(X86_FEATURE_RDTSCP);
> + case MSR_IA32_BNDCFGS:
> + return false;
> default:
> break;
> }
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 9588914e941e..dbeef64f7409 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -6279,6 +6279,8 @@ static bool vmx_has_virtualized_msr(u32 index)
> switch (index) {
> case MSR_TSC_AUX:
> return cpu_has_vmx_rdtscp();
> + case MSR_IA32_BNDCFGS:
> + return kvm_mpx_supported();
> default:
> break;
> }
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a8619c52ea86..70cbb9164088 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5237,10 +5237,6 @@ static void kvm_init_msr_list(void)
> * to the guests in some cases.
> */
> switch (msr_index) {
> - case MSR_IA32_BNDCFGS:
> - if (!kvm_mpx_supported())
> - continue;
> - break;
> case MSR_IA32_RTIT_CTL:
> case MSR_IA32_RTIT_STATUS:
> if (!kvm_x86_ops->pt_supported())

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

--
Vitaly