Re: [PATCH v2 19/43] KVM: Add helpers to wake/query blocking vCPU

From: Maxim Levitsky <mlevitsk@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
	Marc Zyngier <maz@kernel.org>,
	Huacai Chen <chenhuacai@kernel.org>,
	Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
	Paul Mackerras <paulus@ozlabs.org>,
	Anup Patel <anup.patel@wdc.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Cc: James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Atish Patra <atish.patra@wdc.com>,
	David Hildenbrand <david@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org,
	kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
	kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, David Matlack <dmatlack@google.com>,
	Oliver Upton <oupton@google.com>,
	Jing Zhang <jingzhangos@google.com>
Subject: Re: [PATCH v2 19/43] KVM: Add helpers to wake/query blocking vCPU
Date: Wed, 27 Oct 2021 22:27:22 +0300	[thread overview]
Message-ID: <495f9106220b87ffa9eaf15fcf39b950628adee1.camel@redhat.com> (raw)
In-Reply-To: <20211009021236.4122790-20-seanjc@google.com>

On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote:
> Add helpers to wake and query a blocking vCPU.  In addition to providing
> nice names, the helpers reduce the probability of KVM neglecting to use
> kvm_arch_vcpu_get_wait().
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/arm64/kvm/arch_timer.c |  3 +--
>  arch/arm64/kvm/arm.c        |  2 +-
>  arch/x86/kvm/lapic.c        |  2 +-
>  include/linux/kvm_host.h    | 14 ++++++++++++++
>  virt/kvm/async_pf.c         |  2 +-
>  virt/kvm/kvm_main.c         |  8 ++------
>  6 files changed, 20 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
> index 7e8396f74010..addd53b6eba6 100644
> --- a/arch/arm64/kvm/arch_timer.c
> +++ b/arch/arm64/kvm/arch_timer.c
> @@ -649,7 +649,6 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
>  {
>  	struct arch_timer_cpu *timer = vcpu_timer(vcpu);
>  	struct timer_map map;
> -	struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
>  
>  	if (unlikely(!timer->enabled))
>  		return;
> @@ -672,7 +671,7 @@ void kvm_timer_vcpu_put(struct kvm_vcpu *vcpu)
>  	if (map.emul_ptimer)
>  		soft_timer_cancel(&map.emul_ptimer->hrtimer);
>  
> -	if (rcuwait_active(wait))
> +	if (kvm_vcpu_is_blocking(vcpu))
>  		kvm_timer_blocking(vcpu);
>  
>  	/*
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 268b1e7bf700..9ff0e85a9f16 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -622,7 +622,7 @@ void kvm_arm_resume_guest(struct kvm *kvm)
>  
>  	kvm_for_each_vcpu(i, vcpu, kvm) {
>  		vcpu->arch.pause = false;
> -		rcuwait_wake_up(kvm_arch_vcpu_get_wait(vcpu));
> +		__kvm_vcpu_wake_up(vcpu);
>  	}
>  }
>  
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 76fb00921203..0cd7ed21b205 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -1931,7 +1931,7 @@ void kvm_lapic_expired_hv_timer(struct kvm_vcpu *vcpu)
>  	/* If the preempt notifier has already run, it also called apic_timer_expired */
>  	if (!apic->lapic_timer.hv_timer_in_use)
>  		goto out;
> -	WARN_ON(rcuwait_active(&vcpu->wait));
> +	WARN_ON(kvm_vcpu_is_blocking(vcpu));
>  	apic_timer_expired(apic, false);
>  	cancel_hv_timer(apic);
>  
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index bdaa0e70b060..1fa38dc00b87 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1151,6 +1151,20 @@ static inline struct rcuwait *kvm_arch_vcpu_get_wait(struct kvm_vcpu *vcpu)
>  #endif
>  }
>  
> +/*
> + * Wake a vCPU if necessary, but don't do any stats/metadata updates.  Returns
> + * true if the vCPU was blocking and was awakened, false otherwise.
> + */
> +static inline bool __kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
> +{
> +	return !!rcuwait_wake_up(kvm_arch_vcpu_get_wait(vcpu));
> +}
> +
> +static inline bool kvm_vcpu_is_blocking(struct kvm_vcpu *vcpu)
> +{
> +	return rcuwait_active(kvm_arch_vcpu_get_wait(vcpu));
> +}
> +
>  #ifdef __KVM_HAVE_ARCH_INTC_INITIALIZED
>  /*
>   * returns true if the virtual interrupt controller is initialized and
> diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
> index ccb35c22785e..9bfe1d6f6529 100644
> --- a/virt/kvm/async_pf.c
> +++ b/virt/kvm/async_pf.c
> @@ -85,7 +85,7 @@ static void async_pf_execute(struct work_struct *work)
>  
>  	trace_kvm_async_pf_completed(addr, cr2_or_gpa);
>  
> -	rcuwait_wake_up(kvm_arch_vcpu_get_wait(vcpu));
> +	__kvm_vcpu_wake_up(vcpu);
>  
>  	mmput(mm);
>  	kvm_put_kvm(vcpu->kvm);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 481e8178b43d..c870cae7e776 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -3332,10 +3332,7 @@ EXPORT_SYMBOL_GPL(kvm_vcpu_halt);
>  
>  bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
>  {
> -	struct rcuwait *waitp;
> -
> -	waitp = kvm_arch_vcpu_get_wait(vcpu);
> -	if (rcuwait_wake_up(waitp)) {
> +	if (__kvm_vcpu_wake_up(vcpu)) {
>  		WRITE_ONCE(vcpu->ready, true);
>  		++vcpu->stat.generic.halt_wakeup;
>  		return true;
> @@ -3490,8 +3487,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
>  				continue;
>  			if (vcpu == me)
>  				continue;
> -			if (rcuwait_active(kvm_arch_vcpu_get_wait(vcpu)) &&
> -			    !vcpu_dy_runnable(vcpu))
> +			if (kvm_vcpu_is_blocking(vcpu) && !vcpu_dy_runnable(vcpu))
>  				continue;
>  			if (READ_ONCE(vcpu->preempted) && yield_to_kernel_mode &&
>  			    !kvm_arch_dy_has_pending_interrupt(vcpu) &&

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>