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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Date:   Thu, 16 Jan 2020 09:55:57 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Liran Alon <liran.alon@...cle.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

Liran Alon <liran.alon@...cle.com> writes:

>> 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?
>

Because error messages I add are both human readable and conform to SDM!
:-)

On a more serious not yes, we should probably do that. We may even want
to use it in non-nesting (and non VMX) code in KVM.

Thanks,

-- 
Vitaly