linux-kernel - Re: [PATCH v2 12/43] KVM: x86: Tweak halt emulation helper names to free up kvm_vcpu

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Message-ID: <e04b75455437da29fb009668e60b5be1732a183b.camel@redhat.com>
Date:   Wed, 27 Oct 2021 17:18:30 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Atish Patra <atish.patra@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        David Matlack <dmatlack@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>
Subject: Re: [PATCH v2 12/43] KVM: x86: Tweak halt emulation helper names to
 free up kvm_vcpu_halt()

On Wed, 2021-10-27 at 17:10 +0300, Maxim Levitsky wrote:
> On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote:
> > Rename a variety of HLT-related helpers to free up the function name
> > "kvm_vcpu_halt" for future use in generic KVM code, e.g. to differentiate
> > between "block" and "halt".
> > 
> > No functional change intended.
> > 
> > Reviewed-by: David Matlack <dmatlack@...gle.com>
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >  arch/x86/include/asm/kvm_host.h |  2 +-
> >  arch/x86/kvm/vmx/nested.c       |  2 +-
> >  arch/x86/kvm/vmx/vmx.c          |  4 ++--
> >  arch/x86/kvm/x86.c              | 13 +++++++------
> >  4 files changed, 11 insertions(+), 10 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 7aafc27ce7a9..328103a520d3 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1689,7 +1689,7 @@ int kvm_emulate_monitor(struct kvm_vcpu *vcpu);
> >  int kvm_fast_pio(struct kvm_vcpu *vcpu, int size, unsigned short port, int in);
> >  int kvm_emulate_cpuid(struct kvm_vcpu *vcpu);
> >  int kvm_emulate_halt(struct kvm_vcpu *vcpu);
> > -int kvm_vcpu_halt(struct kvm_vcpu *vcpu);
> > +int kvm_emulate_halt_noskip(struct kvm_vcpu *vcpu);
> >  int kvm_emulate_ap_reset_hold(struct kvm_vcpu *vcpu);
> >  int kvm_emulate_wbinvd(struct kvm_vcpu *vcpu);
> >  
> > diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> > index af1bbb73430a..d0237a441feb 100644
> > --- a/arch/x86/kvm/vmx/nested.c
> > +++ b/arch/x86/kvm/vmx/nested.c
> > @@ -3619,7 +3619,7 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
> >  		    !(nested_cpu_has(vmcs12, CPU_BASED_INTR_WINDOW_EXITING) &&
> >  		      (vmcs12->guest_rflags & X86_EFLAGS_IF))) {
> >  			vmx->nested.nested_run_pending = 0;
> > -			return kvm_vcpu_halt(vcpu);
> > +			return kvm_emulate_halt_noskip(vcpu);
> >  		}
> >  		break;
> >  	case GUEST_ACTIVITY_WAIT_SIPI:
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index 1c8b2b6e7ed9..5517893f12fc 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -4741,7 +4741,7 @@ static int handle_rmode_exception(struct kvm_vcpu *vcpu,
> >  		if (kvm_emulate_instruction(vcpu, 0)) {
> >  			if (vcpu->arch.halt_request) {
> >  				vcpu->arch.halt_request = 0;
> > -				return kvm_vcpu_halt(vcpu);
> > +				return kvm_emulate_halt_noskip(vcpu);
> 
> Could you elaborate on why you choose _noskip suffix? 
>  
> As far as I see, kvm_vcpu_halt just calls __kvm_vcpu_halt with new VCPU run state/exit reason,
> which is used only when local apic is not in the kernel (which is these days not that
> supported configuration).
> 
> Other user of __kvm_vcpu_halt is something SEV related.
>  
> Best regards,
> 	Maxim Levitsky
> 
> 
> >  			}
> >  			return 1;
> >  		}
> > @@ -5415,7 +5415,7 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
> >  
> >  		if (vcpu->arch.halt_request) {
> >  			vcpu->arch.halt_request = 0;
> > -			return kvm_vcpu_halt(vcpu);
> > +			return kvm_emulate_halt_noskip(vcpu);
> >  		}
> >  
> >  		/*
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 4a52a08707de..9c23ae1d483d 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -8649,7 +8649,7 @@ void kvm_arch_exit(void)
> >  #endif
> >  }
> >  
> > -static int __kvm_vcpu_halt(struct kvm_vcpu *vcpu, int state, int reason)
> > +static int __kvm_emulate_halt(struct kvm_vcpu *vcpu, int state, int reason)
> >  {
> >  	++vcpu->stat.halt_exits;
> >  	if (lapic_in_kernel(vcpu)) {
> > @@ -8661,11 +8661,11 @@ static int __kvm_vcpu_halt(struct kvm_vcpu *vcpu, int state, int reason)
> >  	}
> >  }
> >  
> > -int kvm_vcpu_halt(struct kvm_vcpu *vcpu)
> > +int kvm_emulate_halt_noskip(struct kvm_vcpu *vcpu)
> >  {
> > -	return __kvm_vcpu_halt(vcpu, KVM_MP_STATE_HALTED, KVM_EXIT_HLT);
> > +	return __kvm_emulate_halt(vcpu, KVM_MP_STATE_HALTED, KVM_EXIT_HLT);
> >  }
> > -EXPORT_SYMBOL_GPL(kvm_vcpu_halt);
> > +EXPORT_SYMBOL_GPL(kvm_emulate_halt_noskip);
> >  
> >  int kvm_emulate_halt(struct kvm_vcpu *vcpu)
> >  {
> > @@ -8674,7 +8674,7 @@ int kvm_emulate_halt(struct kvm_vcpu *vcpu)
> >  	 * TODO: we might be squashing a GUESTDBG_SINGLESTEP-triggered
> >  	 * KVM_EXIT_DEBUG here.
> >  	 */
> > -	return kvm_vcpu_halt(vcpu) && ret;
> > +	return kvm_emulate_halt_noskip(vcpu) && ret;
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_emulate_halt);
> >  
> > @@ -8682,7 +8682,8 @@ int kvm_emulate_ap_reset_hold(struct kvm_vcpu *vcpu)
> >  {
> >  	int ret = kvm_skip_emulated_instruction(vcpu);
> >  
> > -	return __kvm_vcpu_halt(vcpu, KVM_MP_STATE_AP_RESET_HOLD, KVM_EXIT_AP_RESET_HOLD) && ret;
> > +	return __kvm_emulate_halt(vcpu, KVM_MP_STATE_AP_RESET_HOLD,
> > +					KVM_EXIT_AP_RESET_HOLD) && ret;
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_emulate_ap_reset_hold);
> >  

Also while at it, why not to use say '__kvm_emulate_hlt' ('hlt' instead of 'halt') to 
put emphasis on the fact that we are emulating a cpu instruction?

Best regards,
	Maxim Levitsky