Re: [PATCH v4 02/11] KVM: add kvm_request_pending

From: Christoffer Dall <cdall@linaro.org>
To: Andrew Jones <drjones@redhat.com>
Cc: marc.zyngier@arm.com, pbonzini@redhat.com,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Subject: Re: [PATCH v4 02/11] KVM: add kvm_request_pending
Date: Thu, 1 Jun 2017 12:35:04 +0200	[thread overview]
Message-ID: <20170601103504.GC20919@cbox> (raw)
In-Reply-To: <20170516022035.7674-3-drjones@redhat.com>

On Tue, May 16, 2017 at 04:20:26AM +0200, Andrew Jones wrote:
> From: Radim Krčmář <rkrcmar@redhat.com>
> 
> A first step in vcpu->requests encapsulation.  Additionally, we now
> use READ_ONCE() when accessing vcpu->requests, which ensures we
> always load vcpu->requests when it's accessed.  This is important as
> other threads can change it any time.  Also, READ_ONCE() documents
> that vcpu->requests is used with other threads, likely requiring
> memory barriers, which it does.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> [ Documented the new use of READ_ONCE() and converted another check
>   in arch/mips/kvm/vz.c ]
> Signed-off-by: Andrew Jones <drjones@redhat.com>

Acked-by: Christoffer Dall <cdall@linaro.org>

> ---
>  arch/mips/kvm/trap_emul.c  | 2 +-
>  arch/mips/kvm/vz.c         | 2 +-
>  arch/powerpc/kvm/booke.c   | 2 +-
>  arch/powerpc/kvm/powerpc.c | 5 ++---
>  arch/s390/kvm/kvm-s390.c   | 2 +-
>  arch/x86/kvm/x86.c         | 4 ++--
>  include/linux/kvm_host.h   | 5 +++++
>  7 files changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/mips/kvm/trap_emul.c b/arch/mips/kvm/trap_emul.c
> index a563759fd142..6a0d7040d882 100644
> --- a/arch/mips/kvm/trap_emul.c
> +++ b/arch/mips/kvm/trap_emul.c
> @@ -1094,7 +1094,7 @@ static void kvm_trap_emul_check_requests(struct kvm_vcpu *vcpu, int cpu,
>  	struct mm_struct *mm;
>  	int i;
>  
> -	if (likely(!vcpu->requests))
> +	if (likely(!kvm_request_pending(vcpu)))
>  		return;
>  
>  	if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu)) {
> diff --git a/arch/mips/kvm/vz.c b/arch/mips/kvm/vz.c
> index 71d8856ade64..74805035edc8 100644
> --- a/arch/mips/kvm/vz.c
> +++ b/arch/mips/kvm/vz.c
> @@ -2337,7 +2337,7 @@ static int kvm_vz_check_requests(struct kvm_vcpu *vcpu, int cpu)
>  	int ret = 0;
>  	int i;
>  
> -	if (!vcpu->requests)
> +	if (!kvm_request_pending(vcpu))
>  		return 0;
>  
>  	if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu)) {
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index 3eaac3809977..071b87ee682f 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -687,7 +687,7 @@ int kvmppc_core_prepare_to_enter(struct kvm_vcpu *vcpu)
>  
>  	kvmppc_core_check_exceptions(vcpu);
>  
> -	if (vcpu->requests) {
> +	if (kvm_request_pending(vcpu)) {
>  		/* Exception delivery raised request; start over */
>  		return 1;
>  	}
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index f7cf2cd564ef..fd64f087737c 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -55,8 +55,7 @@ EXPORT_SYMBOL_GPL(kvmppc_pr_ops);
>  
>  int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
>  {
> -	return !!(v->arch.pending_exceptions) ||
> -	       v->requests;
> +	return !!(v->arch.pending_exceptions) || kvm_request_pending(v);
>  }
>  
>  int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
> @@ -108,7 +107,7 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
>  		 */
>  		smp_mb();
>  
> -		if (vcpu->requests) {
> +		if (kvm_request_pending(vcpu)) {
>  			/* Make sure we process requests preemptable */
>  			local_irq_enable();
>  			trace_kvm_check_requests(vcpu);
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 689ac48361c6..ad41e0fa3a21 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2440,7 +2440,7 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
>  {
>  retry:
>  	kvm_s390_vcpu_request_handled(vcpu);
> -	if (!vcpu->requests)
> +	if (!kvm_request_pending(vcpu))
>  		return 0;
>  	/*
>  	 * We use MMU_RELOAD just to re-arm the ipte notifier for the
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 464da936c53d..f81060518635 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6710,7 +6710,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  
>  	bool req_immediate_exit = false;
>  
> -	if (vcpu->requests) {
> +	if (kvm_request_pending(vcpu)) {
>  		if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
>  			kvm_mmu_unload(vcpu);
>  		if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
> @@ -6874,7 +6874,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  			kvm_x86_ops->sync_pir_to_irr(vcpu);
>  	}
>  
> -	if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
> +	if (vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu)
>  	    || need_resched() || signal_pending(current)) {
>  		vcpu->mode = OUTSIDE_GUEST_MODE;
>  		smp_wmb();
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 3724b51aab64..0b50e7b35ed4 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1105,6 +1105,11 @@ static inline void kvm_make_request(int req, struct kvm_vcpu *vcpu)
>  	set_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
>  }
>  
> +static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
> +{
> +	return READ_ONCE(vcpu->requests);
> +}
> +
>  static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
>  {
>  	return test_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
> -- 
> 2.9.3
> 
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