Re: [PATCH RFC 3/3] x86/kvm/hyper-v: don't allow to turn on unsupported VMX controls for nested guests

Liran Alon
2020-01-15T22:59:28Z

> On 15 Jan 2020, at 19:10, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Sane L1 hypervisors are not supposed to turn any of the unsupported VMX
> controls on for its guests and nested_vmx_check_controls() checks for
> that. This is, however, not the case for the controls which are supported
> on the host but are missing in enlightened VMCS and when eVMCS is in use.
>
> It would certainly be possible to add these missing checks to
> nested_check_vm_execution_controls()/_vm_exit_controls()/.. but it seems
> preferable to keep eVMCS-specific stuff in eVMCS and reduce the impact on
> non-eVMCS guests by doing less unrelated checks. Create a separate
> nested_evmcs_check_controls() for this purpose.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/vmx/evmcs.c | 56 ++++++++++++++++++++++++++++++++++++++-
> arch/x86/kvm/vmx/evmcs.h | 1 +
> arch/x86/kvm/vmx/nested.c | 3 +++
> 3 files changed, 59 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/evmcs.c b/arch/x86/kvm/vmx/evmcs.c
> index b5d6582ba589..88f462866396 100644
> --- a/arch/x86/kvm/vmx/evmcs.c
> +++ b/arch/x86/kvm/vmx/evmcs.c
> @@ -4,9 +4,11 @@
> #include <linux/smp.h>
>
> #include "../hyperv.h"
> -#include "evmcs.h"
> #include "vmcs.h"
> +#include "vmcs12.h"
> +#include "evmcs.h"
> #include "vmx.h"
> +#include "trace.h"
>
> DEFINE_STATIC_KEY_FALSE(enable_evmcs);
>
> @@ -378,6 +380,58 @@ void nested_evmcs_filter_control_msr(u32 msr_index, u64 *pdata)
> *pdata = ctl_low | ((u64)ctl_high << 32);
> }
>
> +int nested_evmcs_check_controls(struct vmcs12 *vmcs12)
> +{
> + int ret = 0;
> + u32 unsupp_ctl;
> +
> + unsupp_ctl = vmcs12->pin_based_vm_exec_control &
> + EVMCS1_UNSUPPORTED_PINCTRL;
> + if (unsupp_ctl) {
> + trace_kvm_nested_vmenter_failed(
> + "eVMCS: unsupported pin-based VM-execution controls",
> + unsupp_ctl);

Why not move "CC” macro from nested.c to nested.h and use it here as-well instead of replicating it’s logic?

-Liran