On Fri, Apr 27, 2012 at 04:15:35PM +0530, Raghavendra K T wrote:
> On 04/24/2012 03:29 PM, Gleb Natapov wrote:
> >On Mon, Apr 23, 2012 at 03:29:47PM +0530, Raghavendra K T wrote:
> >>From: Srivatsa Vaddagiri<vatsa@xxxxxxxxxxxxxxxxxx>
> >>
> >>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@xxxxxxxxxxxxxxxxxx>
> >>Signed-off-by: Suzuki Poulose<suzuki@xxxxxxxxxx>
> >>Signed-off-by: Raghavendra K T<raghavendra.kt@xxxxxxxxxxxxxxxxxx>
> >>---
> [...]
> >>+/*
> >>+ * 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();
> >>+ kvm_vcpu_kick(vcpu);
> >>+ }
> >>+}
> >This is too similar to kvm_irq_delivery_to_apic(). Why not reuse it. We
> >can use one of reserved delivery modes as PV delivery mode. We will
> >disallow guest to trigger it through apic interface, so this will not be
> >part of ABI and can be changed at will.
> >
>
> I think it is interesting ( Perhaps more reasonable way of doing it).
> I am not too familiar with lapic source. So, pardon me if my
> questions are stupid.
>
> Something like below is what I deciphered from your suggestion which
> is working.
>
> kvm/x86.c
> =========
> kvm_pv_kick_cpu_op()
> {
>
> struct kvm_lapic_irq lapic_irq;
>
> lapic_irq.shorthand = 0;
> lapic_irq.dest_mode = 0;
> lapic_irq.dest_id = apicid;
>
> lapic_irq.delivery_mode = PV_DELIVERY_MODE;
> kvm_irq_delivery_to_apic(kvm, 0, &lapic_irq );
>
> }
>
> kvm/lapic.c
> ==========
> _apic_accept_irq()
> {
> ...
> case APIC_DM_REMRD:
> result = 1;
> vcpu->pv_unhalted = 1
> smp_mb();
> kvm_make_request(KVM_REQ_EVENT, vcpu);
> kvm_vcpu_kick(vcpu);
> break;
>
> ...
> }
>
> here using PV_DELIVERY_MODE = APIC_DM_REMRD, which was unused.
>
Yes, this is what I mean except that PV_DELIVERY_MODE should be
number defined as reserved by Intel spec.
> OR
> 1) Are you asking to remove vcpu->pv_unhalted flag and replace with an irq?
I would like to remove vcpu->pv_unhalted, but do not see how to do that,
so I do not asking that :)
> 2) are you talking about some reserved fields in struct local_apic instead
> of APIC_DM_REMRD what I have used above?
Delivery modes 011b and 111b are reserved. We can use one if them.
> [ Honestly, arch/x86/include/asm/apicdef.h had too much of info to
> digest :( ]
>
> 3) I am not sure about: disallow guest to trigger it through apic
> interface part also.(mean howto?)
I mean we should disallow guest to set delivery mode to reserved values
through apic interface.
> 4) And one more question, So you think it takes care of migration part
> (in case we are removing pv_unhalted flag)?
No, since I am not asking for removing pv_unhalted flag. I want to reuse
code that we already have to deliver the unhalt event.
>
> It would be helpful if you can give little more explanation/ pointer
> to Documentation.
>
> Ingo is keen to see whole ticketlock/Xen/KVM patch in one go.
> and anyhow since this does not cause any ABI change, I hope you
> don't mind if
> I do only the vcpu->pv_unhalted change you suggested now [ having
> pv_unhalted reset in vcpu_run if
> you meant something else than code I have above ], so that whole
> series get fair amount time for testing.
--
Gleb.
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