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

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Message-Id: <CF37ED31-4ED0-45C2-A309-3E1E2C2E54F8@oracle.com>
Date:   Thu, 16 Jan 2020 00:59:15 +0200
From:   Liran Alon <liran.alon@...cle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, Roman Kagan <rkagan@...tuozzo.com>
Subject: Re: [PATCH RFC 3/3] x86/kvm/hyper-v: don't allow to turn on
 unsupported VMX controls for nested guests



> On 15 Jan 2020, at 19:10, Vitaly Kuznetsov <vkuznets@...hat.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@...hat.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