linux-kernel - Re: [PATCH v2 10/11] KVM: SVM: implement support for vNMI

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Message-ID: <6f7fec84-1915-4499-104d-d29bf78270b5@amd.com>
Date:   Fri, 10 Feb 2023 17:32:55 +0530
From:   Santosh Shukla <santosh.shukla@....com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, Sandipan Das <sandipan.das@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Jiaxi Chen <jiaxi.chen@...ux.intel.com>,
        Babu Moger <babu.moger@....com>, linux-kernel@...r.kernel.org,
        Jing Liu <jing2.liu@...el.com>,
        Wyes Karny <wyes.karny@....com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Santosh Shukla <santosh.shukla@....com>
Subject: Re: [PATCH v2 10/11] KVM: SVM: implement support for vNMI

On 1/28/2023 6:40 AM, Sean Christopherson wrote:
> On Tue, Nov 29, 2022, Maxim Levitsky wrote:
>> This patch implements support for injecting pending
>> NMIs via the .kvm_x86_set_hw_nmi_pending using new AMD's vNMI
>> feature.
>>
>> Note that the vNMI can't cause a VM exit, which is needed
>> when a nested guest intercepts NMIs.
>>
>> Therefore to avoid breaking nesting, the vNMI is inhibited while
>> a nested guest is running and instead, the legacy NMI window
>> detection and delivery method is used.
>>
>> While it is possible to passthrough the vNMI if a nested guest
>> doesn't intercept NMIs, such usage is very uncommon, and it's
>> not worth to optimize for.
>>
>> Signed-off-by: Santosh Shukla <santosh.shukla@....com>
>> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
>> ---
>>  arch/x86/kvm/svm/nested.c |  42 +++++++++++++++
>>  arch/x86/kvm/svm/svm.c    | 111 ++++++++++++++++++++++++++++++--------
>>  arch/x86/kvm/svm/svm.h    |  10 ++++
>>  3 files changed, 140 insertions(+), 23 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
>> index e891318595113e..5bea672bf8b12d 100644
>> --- a/arch/x86/kvm/svm/nested.c
>> +++ b/arch/x86/kvm/svm/nested.c
>> @@ -623,6 +623,42 @@ static bool is_evtinj_nmi(u32 evtinj)
>>  	return type == SVM_EVTINJ_TYPE_NMI;
>>  }
>>  
>> +static void nested_svm_save_vnmi(struct vcpu_svm *svm)
>> +{
>> +	struct vmcb *vmcb01 = svm->vmcb01.ptr;
>> +
>> +	/*
>> +	 * Copy the vNMI state back to software NMI tracking state
>> +	 * for the duration of the nested run
>> +	 */
>> +
> 
> Unecessary newline.
> 
ok.

>> +	svm->nmi_masked = vmcb01->control.int_ctl & V_NMI_MASK;
>> +	svm->vcpu.arch.nmi_pending += vmcb01->control.int_ctl & V_NMI_PENDING;
>> +}
>> +
>> +static void nested_svm_restore_vnmi(struct vcpu_svm *svm)
>> +{
>> +	struct kvm_vcpu *vcpu = &svm->vcpu;
>> +	struct vmcb *vmcb01 = svm->vmcb01.ptr;
>> +
>> +	/*
>> +	 * Restore the vNMI state from the software NMI tracking state
>> +	 * after a nested run
>> +	 */
>> +
> 
> Unnecessary newline.
>

ok.
 
>> +	if (svm->nmi_masked)
>> +		vmcb01->control.int_ctl |= V_NMI_MASK;
>> +	else
>> +		vmcb01->control.int_ctl &= ~V_NMI_MASK;
>> +
>> +	if (vcpu->arch.nmi_pending) {
>> +		vcpu->arch.nmi_pending--;
>> +		vmcb01->control.int_ctl |= V_NMI_PENDING;
>> +	} else
>> +		vmcb01->control.int_ctl &= ~V_NMI_PENDING;
> 
> Needs curly braces.
> 
Yes.

Thanks,
Santosh