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Subject: Re: [PATCH RFC 3/3] x86/kvm/hyper-v: don't allow to turn on
 unsupported VMX controls for nested guests
From:   Liran Alon <liran.alon@oracle.com>
In-Reply-To: <20200115171014.56405-4-vkuznets@redhat.com>
Date:   Thu, 16 Jan 2020 00:59:15 +0200
Cc:     kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Jim Mattson <jmattson@google.com>,
        linux-kernel@vger.kernel.org, Roman Kagan <rkagan@virtuozzo.com>
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Message-Id: <CF37ED31-4ED0-45C2-A309-3E1E2C2E54F8@oracle.com>
References: <20200115171014.56405-1-vkuznets@redhat.com>
 <20200115171014.56405-4-vkuznets@redhat.com>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On 15 Jan 2020, at 19:10, Vitaly Kuznetsov <vkuznets@redhat.com> =
wrote:
>=20
> 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.
>=20
> 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.
>=20
> 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(-)
>=20
> 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>
>=20
> #include "../hyperv.h"
> -#include "evmcs.h"
> #include "vmcs.h"
> +#include "vmcs12.h"
> +#include "evmcs.h"
> #include "vmx.h"
> +#include "trace.h"
>=20
> DEFINE_STATIC_KEY_FALSE(enable_evmcs);
>=20
> @@ -378,6 +380,58 @@ void nested_evmcs_filter_control_msr(u32 =
msr_index, u64 *pdata)
> 	*pdata =3D ctl_low | ((u64)ctl_high << 32);
> }
>=20
> +int nested_evmcs_check_controls(struct vmcs12 *vmcs12)
> +{
> +	int ret =3D 0;
> +	u32 unsupp_ctl;
> +
> +	unsupp_ctl =3D 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=E2=80=9D macro from nested.c to nested.h and use it =
here as-well instead of replicating it=E2=80=99s logic?

-Liran