linux-kernel - Re: [PATCH RFC V10 12/18] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

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Date:	Mon, 15 Jul 2013 11:23:26 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	mingo@...hat.com, jeremy@...p.org, x86@...nel.org,
	konrad.wilk@...cle.com, hpa@...or.com, pbonzini@...hat.com,
	linux-doc@...r.kernel.org, habanero@...ux.vnet.ibm.com,
	xen-devel@...ts.xensource.com, peterz@...radead.org,
	mtosatti@...hat.com, stefano.stabellini@...citrix.com,
	andi@...stfloor.org, attilio.rao@...rix.com, ouyang@...pitt.edu,
	gregkh@...e.de, agraf@...e.de, chegu_vinod@...com,
	torvalds@...ux-foundation.org, avi.kivity@...il.com,
	tglx@...utronix.de, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, stephan.diestelhorst@....com,
	riel@...hat.com, drjones@...hat.com,
	virtualization@...ts.linux-foundation.org,
	srivatsa.vaddagiri@...il.com
Subject: Re: [PATCH RFC V10 12/18] kvm hypervisor : Add a hypercall to KVM
 hypervisor to support pv-ticketlocks

On 07/14/2013 07:18 PM, Gleb Natapov wrote:
> On Mon, Jun 24, 2013 at 06:13:04PM +0530, Raghavendra K T wrote:
>> kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks
>>
>> 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.
>>
>> Signed-off-by: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
>> Signed-off-by: Suzuki Poulose <suzuki@...ibm.com>
>> [Raghu: Apic related changes, folding pvunhalted into vcpu_runnable]
>> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
>> ---
>>   arch/x86/include/asm/kvm_host.h      |    5 +++++
>>   arch/x86/include/uapi/asm/kvm_para.h |    1 +
>>   arch/x86/kvm/cpuid.c                 |    3 ++-
>>   arch/x86/kvm/x86.c                   |   37 ++++++++++++++++++++++++++++++++++
>>   include/uapi/linux/kvm_para.h        |    1 +
>>   5 files changed, 46 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 3741c65..95702de 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -503,6 +503,11 @@ struct kvm_vcpu_arch {
>>   	 * instruction.
>>   	 */
>>   	bool write_fault_to_shadow_pgtable;
>> +
>> +	/* pv related host specific info */
>> +	struct {
>> +		bool pv_unhalted;
>> +	} pv;
>>   };
>>
>>   struct kvm_lpage_info {
>> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
>> index 06fdbd9..94dc8ca 100644
>> --- a/arch/x86/include/uapi/asm/kvm_para.h
>> +++ b/arch/x86/include/uapi/asm/kvm_para.h
>> @@ -23,6 +23,7 @@
>>   #define KVM_FEATURE_ASYNC_PF		4
>>   #define KVM_FEATURE_STEAL_TIME		5
>>   #define KVM_FEATURE_PV_EOI		6
>> +#define KVM_FEATURE_PV_UNHALT		7
>>
>>   /* The last 8 bits are used to indicate how to interpret the flags field
>>    * in pvclock structure. If no bits are set, all flags are ignored.
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index a20ecb5..b110fe6 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -413,7 +413,8 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>>   			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
>>   			     (1 << KVM_FEATURE_ASYNC_PF) |
>>   			     (1 << KVM_FEATURE_PV_EOI) |
>> -			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
>> +			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT) |
>> +			     (1 << KVM_FEATURE_PV_UNHALT);
>>
>>   		if (sched_info_on())
>>   			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 094b5d9..f8bea30 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -5449,6 +5449,36 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
>>   	return 1;
>>   }
>>
>> +/*
>> + * 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 = true;
>> +		/* We need everybody see unhalt before vcpu unblocks */
>> +		smp_wmb();
>> +		kvm_vcpu_kick(vcpu);
>> +	}
>> +}
>> +
>>   int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>>   {
>>   	unsigned long nr, a0, a1, a2, a3, ret;
>> @@ -5482,6 +5512,10 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>>   	case KVM_HC_VAPIC_POLL_IRQ:
>>   		ret = 0;
>>   		break;
>> +	case KVM_HC_KICK_CPU:
>> +		kvm_pv_kick_cpu_op(vcpu->kvm, a0);
> Lets make it hypercall with two parameters:
> a0 - flags
> a1 - apic id of a cpu to kick
>
> A0 have to be zero. This will make it more extensible.

Good point. 'll incorporate that.


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