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

[Xin Li]

On 7/1/2024 8:45 AM, Jacob Pan wrote:
> On Fri, 28 Jun 2024 21:07:04 -0700, Xin Li <xin@xxxxxxxxx> wrote:
>
> > On 6/28/2024 1:18 PM, Jacob Pan wrote:
> > > From: Zeng Guang <guang.zeng@xxxxxxxxx>
> > >
> > > 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@xxxxxxxxx>
> > > Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > > ---
> > >    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