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

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Date: Fri, 28 Jun 2024 21:07:04 -0700
From: Xin Li <xin@...or.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>, 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>
Cc: 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 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.

> 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))?

> +		} else {
>   			vmx_do_nmi_irqoff();
> +		}
>   		kvm_after_interrupt(vcpu);
>   	}
>