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Date: Wed, 11 Apr 2012 21:29:09 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
X86 <x86@...nel.org>, Avi Kivity <avi@...hat.com>,
Jeremy Fitzhardinge <jeremy@...p.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Greg Kroah-Hartman <gregkh@...e.de>,
Alexander Graf <agraf@...e.de>,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
Gleb Natapov <gleb@...hat.com>,
Randy Dunlap <rdunlap@...otime.net>, linux-doc@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>,
Virtualization <virtualization@...ts.linux-foundation.org>,
Xen <xen-devel@...ts.xensource.com>,
Sasha Levin <levinsasha928@...il.com>,
Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC V5 2/6] kvm hypervisor : Add a hypercall to KVM
hypervisor to support pv-ticketlocks
On Wed, Apr 11, 2012 at 09:06:29PM -0300, Marcelo Tosatti wrote:
> On Fri, Mar 23, 2012 at 01:37:04PM +0530, 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.
> >
> > Signed-off-by: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
> > Signed-off-by: Suzuki Poulose <suzuki@...ibm.com>
> > Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> > ---
> > diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
> > index 734c376..9234f13 100644
> > --- a/arch/x86/include/asm/kvm_para.h
> > +++ b/arch/x86/include/asm/kvm_para.h
> > @@ -16,12 +16,14 @@
> > #define KVM_FEATURE_CLOCKSOURCE 0
> > #define KVM_FEATURE_NOP_IO_DELAY 1
> > #define KVM_FEATURE_MMU_OP 2
> > +
> > /* This indicates that the new set of kvmclock msrs
> > * are available. The use of 0x11 and 0x12 is deprecated
> > */
> > #define KVM_FEATURE_CLOCKSOURCE2 3
> > #define KVM_FEATURE_ASYNC_PF 4
> > #define KVM_FEATURE_STEAL_TIME 5
> > +#define KVM_FEATURE_PV_UNHALT 6
> >
> > /* 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.
> > @@ -32,6 +34,7 @@
> > #define MSR_KVM_SYSTEM_TIME 0x12
> >
> > #define KVM_MSR_ENABLED 1
> > +
> > /* Custom MSRs falls in the range 0x4b564d00-0x4b564dff */
> > #define MSR_KVM_WALL_CLOCK_NEW 0x4b564d00
> > #define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index 89b02bf..61388b9 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -408,7 +408,8 @@ static int do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> > (1 << KVM_FEATURE_NOP_IO_DELAY) |
> > (1 << KVM_FEATURE_CLOCKSOURCE2) |
> > (1 << KVM_FEATURE_ASYNC_PF) |
> > - (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 9cbfc06..bd5ef91 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -2079,6 +2079,7 @@ int kvm_dev_ioctl_check_extension(long ext)
> > case KVM_CAP_XSAVE:
> > case KVM_CAP_ASYNC_PF:
> > case KVM_CAP_GET_TSC_KHZ:
> > + case KVM_CAP_PV_UNHALT:
> > r = 1;
> > break;
> > case KVM_CAP_COALESCED_MMIO:
> > @@ -4913,6 +4914,30 @@ 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) {
> > + vcpu->pv_unhalted = 1;
> > + smp_mb();
> > + kvm_vcpu_kick(vcpu);
> > + }
> > +}
> > +
> > int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
> > {
> > unsigned long nr, a0, a1, a2, a3, ret;
> > @@ -4946,6 +4971,10 @@ 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);
> > + ret = 0;
> > + break;
> > default:
> > ret = -KVM_ENOSYS;
> > break;
> > @@ -6174,6 +6203,7 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
> > !vcpu->arch.apf.halted)
> > || !list_empty_careful(&vcpu->async_pf.done)
> > || vcpu->arch.mp_state == KVM_MP_STATE_SIPI_RECEIVED
> > + || vcpu->pv_unhalted
> > || atomic_read(&vcpu->arch.nmi_queued) ||
> > (kvm_arch_interrupt_allowed(vcpu) &&
> > kvm_cpu_has_interrupt(vcpu));
> > diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> > index 68e67e5..e822d96 100644
> > --- a/include/linux/kvm.h
> > +++ b/include/linux/kvm.h
> > @@ -558,6 +558,7 @@ struct kvm_ppc_pvinfo {
> > #define KVM_CAP_PPC_PAPR 68
> > #define KVM_CAP_S390_GMAP 71
> > #define KVM_CAP_TSC_DEADLINE_TIMER 72
> > +#define KVM_CAP_PV_UNHALT 73
> >
> > #ifdef KVM_CAP_IRQ_ROUTING
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 900c763..433ae97 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -158,6 +158,7 @@ struct kvm_vcpu {
> > #endif
> >
> > struct kvm_vcpu_arch arch;
> > + int pv_unhalted;
> > };
> >
> > static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
> > diff --git a/include/linux/kvm_para.h b/include/linux/kvm_para.h
> > index ff476dd..38226e1 100644
> > --- a/include/linux/kvm_para.h
> > +++ b/include/linux/kvm_para.h
> > @@ -19,6 +19,7 @@
> > #define KVM_HC_MMU_OP 2
> > #define KVM_HC_FEATURES 3
> > #define KVM_HC_PPC_MAP_MAGIC_PAGE 4
> > +#define KVM_HC_KICK_CPU 5
> >
> > /*
> > * hypercalls use architecture specific
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index a91f980..d3b98b1 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -226,6 +226,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
> > vcpu->kvm = kvm;
> > vcpu->vcpu_id = id;
> > vcpu->pid = NULL;
> > + vcpu->pv_unhalted = 0;
> > init_waitqueue_head(&vcpu->wq);
> > kvm_async_pf_vcpu_init(vcpu);
> >
> > @@ -1567,6 +1568,9 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> > prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
> >
> > if (kvm_arch_vcpu_runnable(vcpu)) {
> > + vcpu->pv_unhalted = 0;
> > + /* preventing reordering should be enough here */
> > + barrier();
>
> Is it always OK to erase the notification, even in case an unrelated
> event such as interrupt was the source of wakeup?
Note i am only asking whether it is OK to lose a notification, not
requesting a change to atomic test-and-clear.
It would be nice to have a comment explaining it.
>
> It would be easier to verify that notifications are not lost with atomic
> test_and_clear(pv_unhalted).
>
> Also x86 specific code should remain in arch/x86/kvm/
>
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