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 08:45:58 -0700
From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
To: Xin Li <xin@...or.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>,
 jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v3 07/11] KVM: VMX: Handle NMI Source report in VM exit


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.

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


Thanks,

Jacob