linux-kernel - Re: [PATCH RFC V6 1/5] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

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Message-ID: <4F9D415B.7010103@redhat.com>
Date:	Sun, 29 Apr 2012 16:25:47 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alexander Graf <agraf@...e.de>,
	Randy Dunlap <rdunlap@...otime.net>, linux-doc@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	KVM <kvm@...r.kernel.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	X86 <x86@...nel.org>, Gleb Natapov <gleb@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Xen <xen-devel@...ts.xensource.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC V6 1/5] kvm hypervisor : Add a hypercall to KVM hypervisor
 to support pv-ticketlocks

On 04/23/2012 12:59 PM, Raghavendra K T wrote:
> From: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
>
> KVM_HC_KICK_CPU allows the calling vcpu to kick another vcpu out of halt state.
>     
> The presence of these hypercalls is indicated to guest via
> KVM_FEATURE_PV_UNHALT/KVM_CAP_PV_UNHALT.
>
>  #endif
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index e216ba0..dad475b 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -481,6 +481,10 @@ struct kvm_vcpu_arch {
>  		u64 length;
>  		u64 status;
>  	} osvw;
> +	/* pv related host specific info */
> +	struct {
> +		int pv_unhalted;
> +	} pv;
>  };

'bool'.  Or maybe push into vcpu->requests.

>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4044ce0..7fc9be6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2147,6 +2147,7 @@ int kvm_dev_ioctl_check_extension(long ext)
>  	case KVM_CAP_ASYNC_PF:
>  	case KVM_CAP_GET_TSC_KHZ:
>  	case KVM_CAP_PCI_2_3:
> +	case KVM_CAP_PV_UNHALT:
>  		r = 1;
>  		break;
>  	case KVM_CAP_COALESCED_MMIO:

Redundant, since we can infer this from KVM_GET_SUPPORTED_CPUID.  But
please indicate this in the documentation.

>  
> +/*
> + * kvm_pv_kick_cpu_op:  Kick a vcpu.
> + *
> + * @apicid - apicid of vcpu to be kicked.
> + */
> +static void kvm_pv_kick_cpu_op(struct kvm *kvm, int apicid)
> +{
> +	struct kvm_vcpu *vcpu = NULL;
> +	int i;
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		if (!kvm_apic_present(vcpu))
> +			continue;
> +
> +		if (kvm_apic_match_dest(vcpu, 0, 0, apicid, 0))
> +			break;
> +	}
> +	if (vcpu) {
> +		/*
> +		 * Setting unhalt flag here can result in spurious runnable
> +		 * state when unhalt reset does not happen in vcpu_block.
> +		 * But that is harmless since that should soon result in halt.
> +		 */
> +		vcpu->arch.pv.pv_unhalted = 1;
> +		/* We need everybody see unhalt before vcpu unblocks */
> +		smp_mb();

smp_wmb().

> +		kvm_vcpu_kick(vcpu);
> +	}
> +}
> +
>
>  /*
>   * hypercalls use architecture specific
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 42b7393..edf56d4 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1500,6 +1500,14 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>  		prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
>  
>  		if (kvm_arch_vcpu_runnable(vcpu)) {
> +			/*
> +			 * This is the only safe place to reset unhalt flag.
> +			 * otherwise it results in loosing the notification
> +			 * which eventually can result in vcpu hangs.
> +			 */
> +			kvm_arch_vcpu_reset_pv_unhalted(vcpu);
> +			/* preventing reordering should be enough here */
> +			barrier();
>  			kvm_make_request(KVM_REQ_UNHALT, vcpu);
>  			break;
>  		}
>

Hm, what about reusing KVM_REQ_UNHALT?

-- 
error compiling committee.c: too many arguments to function

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