linux-kernel - Re: [PATCH v3 07/11] KVM: VMX: Handle NMI Source report in VM exit

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Date: Mon, 1 Jul 2024 10:03:58 -0700
From: Xin Li <xin@...or.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc: X86 Kernel <x86@...nel.org>, Sean Christopherson <seanjc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>, "H. Peter Anvin" <hpa@...or.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Xin Li <xin3.li@...el.com>, linux-perf-users@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>, Tony Luck <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>, acme@...nel.org,
        kan.liang@...ux.intel.com, Andi Kleen
 <andi.kleen@...el.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>,
        Zeng Guang <guang.zeng@...el.com>
Subject: Re: [PATCH v3 07/11] KVM: VMX: Handle NMI Source report in VM exit

On 7/1/2024 8:45 AM, Jacob Pan wrote:
> 
> On Fri, 28 Jun 2024 21:07:04 -0700, Xin Li <xin@...or.com> wrote:
> 
>> On 6/28/2024 1:18 PM, Jacob Pan wrote:
>>> From: Zeng Guang <guang.zeng@...el.com>
>>>
>>> If the "NMI exiting" VM-execution control is 1, the value of the 16-bit
>>> NMI source vector is saved in the exit-qualification field in the VMCS
>>> when VM exits occur on CPUs that support NMI source.
>>>
>>> KVM that is aware of NMI-source reporting will push the bitmask of NMI
>>> source vectors as the exceptoin event data field on the stack for then
>>> entry of FRED exception. Subsequently, the host NMI exception handler
>>> is invoked which will process NMI source information in the event data.
>>> This operation is independent of vCPU FRED enabling status.
>>>
>>> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
>>> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>>> ---
>>>    arch/x86/entry/entry_64_fred.S |  2 +-
>>>    arch/x86/kvm/vmx/vmx.c         | 11 ++++++++---
>>>    2 files changed, 9 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/x86/entry/entry_64_fred.S
>>> b/arch/x86/entry/entry_64_fred.S index a02bc6f3d2e6..0d934a3fcaf8 100644
>>> --- a/arch/x86/entry/entry_64_fred.S
>>> +++ b/arch/x86/entry/entry_64_fred.S
>>> @@ -92,7 +92,7 @@ SYM_FUNC_START(asm_fred_entry_from_kvm)
>>>    	 * +--------+-----------------+
>>>    	 */
>>>    	push $0				/* Reserved, must be 0
>>> */
>>> -	push $0				/* Event data, 0 for
>>> IRQ/NMI */
>>> +	push %rsi			/* Event data for IRQ/NMI */
>>>    	push %rdi			/* fred_ss handed in by the
>>> caller */ push %rbp
>>>    	pushf
>>
>> This belongs to the previous patch, it is part of the host changes.
> right, will do.
> 
>>
>>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>>> index 4e7b36081b76..6719c598fa5f 100644
>>> --- a/arch/x86/kvm/vmx/vmx.c
>>> +++ b/arch/x86/kvm/vmx/vmx.c
>>> @@ -7331,10 +7331,15 @@ static noinstr void vmx_vcpu_enter_exit(struct
>>> kvm_vcpu *vcpu, if ((u16)vmx->exit_reason.basic ==
>>> EXIT_REASON_EXCEPTION_NMI && is_nmi(vmx_get_intr_info(vcpu))) {
>>>    		kvm_before_interrupt(vcpu, KVM_HANDLING_NMI);
>>> -		if (cpu_feature_enabled(X86_FEATURE_FRED))
>>> -			fred_entry_from_kvm(EVENT_TYPE_NMI,
>>> NMI_VECTOR, 0);
>>> -		else
>>> +		if (cpu_feature_enabled(X86_FEATURE_FRED)) {
>>> +			unsigned long edata = 0;
>>> +
>>> +			if
>>> (cpu_feature_enabled(X86_FEATURE_NMI_SOURCE))
>>> +				edata = vmx_get_exit_qual(vcpu);
>>> +			fred_entry_from_kvm(EVENT_TYPE_NMI,
>>> NMI_VECTOR, edata);
>>
>> Simply do fred_entry_from_kvm(EVENT_TYPE_NMI, NMI_VECTOR,
>> vmx_get_exit_qual(vcpu))?
> I don't have strong preference but having a local variable improves
> readability IMHO.

My point was, do we actually need this check:
     (cpu_feature_enabled(X86_FEATURE_NMI_SOURCE)?

I don't have a strong preference either.

> 
>>> +		} else {
>>>    			vmx_do_nmi_irqoff();
>>> +		}
>>>    		kvm_after_interrupt(vcpu);
>>>    	}
>>>      
>>
> 
> 
> Thanks,
> 
> Jacob
>