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From: Joao Martins <joao.m.martins@oracle.com>
To: David Woodhouse <dwmw2@infradead.org>,
	Ankur Arora <ankur.a.arora@oracle.com>
Cc: "Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC 10/39] KVM: x86/xen: support upcall vector
Date: Wed, 2 Dec 2020 13:12:07 +0000	[thread overview]
Message-ID: <53baeaa7-0fed-d22c-7767-09ae885d13a0@oracle.com> (raw)
In-Reply-To: <71753a370cd6f9dd147427634284073b78679fa6.camel@infradead.org>

On 12/2/20 11:17 AM, David Woodhouse wrote:
> On Wed, 2019-02-20 at 20:15 +0000, Joao Martins wrote:
>> @@ -176,6 +177,9 @@ int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
>>         int r;
>>  
>>         switch (e->type) {
>> +       case KVM_IRQ_ROUTING_XEN_EVTCHN:
>> +               return kvm_xen_set_evtchn(e, kvm, irq_source_id, level,
>> +                                      line_status);
>>         case KVM_IRQ_ROUTING_HV_SINT:
>>                 return kvm_hv_set_sint(e, kvm, irq_source_id, level,
>>                                        line_status);
>> @@ -325,6 +329,13 @@ int kvm_set_routing_entry(struct kvm *kvm,
>>                 e->hv_sint.vcpu = ue->u.hv_sint.vcpu;
>>                 e->hv_sint.sint = ue->u.hv_sint.sint;
>>                 break;
>> +       case KVM_IRQ_ROUTING_XEN_EVTCHN:
>> +               e->set = kvm_xen_set_evtchn;
>> +               e->evtchn.vcpu = ue->u.evtchn.vcpu;
>> +               e->evtchn.vector = ue->u.evtchn.vector;
>> +               e->evtchn.via = ue->u.evtchn.via;
>> +
>> +               return kvm_xen_setup_evtchn(kvm, e);
>>         default:
>>                 return -EINVAL;
>>         }
> 
> 
> Hmm. I'm not sure I've have done it that way.
> 
> These IRQ routing entries aren't for individual event channel ports;
> they don't map to kvm_xen_evtchn_send().
> 
> They actually represent the upcall to the given vCPU when any event
> channel is signalled, and it's really per-vCPU configuration.
> 
Right.

> When the kernel raises (IPI, VIRQ) events on a given CPU, it doesn't
> actually use these routing entries; it just uses the values in
> vcpu_xen->cb.{via,vector} which were cached from the last of these IRQ
> routing entries that happens to have been processed?
> 
Correct.

> The VMM is *expected* to set up precisely one of these for each vCPU,
> right?
> 
From guest PoV, the hypercall:

	HYPERVISOR_hvm_op(HVMOP_set_param, HVM_PARAM_CALLBACK_IRQ, ...)

(...) is global.

But this one (on more recent versions of Xen, particularly recent Windows guests):

	HVMOP_set_evtchn_upcall_vector

Is per-vCPU, and it's a LAPIC vector.

But indeed the VMM ends up changing the @via @vector on a individual CPU.

> Would it not be better to do that via KVM_XEN_HVM_SET_ATTR?

It's definitely an interesting (better?) alternative, considering we use as a vCPU attribute.

I suppose you're suggesting like,

	KVM_XEN_ATTR_TYPE_CALLBACK

And passing the vector, and callback type.

> The usage model for userspace is presumably that the VMM should set the
> appropriate bit in evtchn_pending, check evtchn_mask and then call into
> the kernel to do the set_irq() to inject the callback vector to the
> guest?
> 
Correct, that's how it works for userspace handled event channels.

> I might be more inclined to go for a model where the kernel handles the
> evtchn_pending/evtchn_mask for us. What would go into the irq routing
> table is { vcpu, port# } which get passed to kvm_xen_evtchn_send().
> 

But passing port to the routing and handling the sending of events wouldn't it lead to
unnecessary handling of event channels which aren't handled by the kernel, compared to
just injecting caring about the upcall?

I thought from previous feedback that it was something you wanted to avoid.

> Does that seem reasonable?
> 
Otherwise, it seems reasonable to have it.

I'll let Ankur chip in too, as this was something he was more closely modelling after.

> Either way, I do think we need a way for events raised in the kernel to
> be signalled to userspace, if they are targeted at a vCPU which has
> CALLBACK_VIA_INTX that the kernel can't do directly. So we probably
> *do* need that eventfd I was objecting to earlier, except that it's not
> a per-evtchn thing; it's per-vCPU.
> 

Ah!

I wanted to mention the GSI callback method too, but wasn't enterily sure if eventfd was
enough.

	Joao

  reply	other threads:[~2020-12-02 13:13 UTC|newest]

Thread overview: 126+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-20 20:15 [PATCH RFC 00/39] x86/KVM: Xen HVM guest support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 01/39] KVM: x86: fix Xen hypercall page msr handling Joao Martins
2019-02-22  1:30   ` Sean Christopherson
2019-02-22 11:47     ` Joao Martins
2019-02-22 12:51     ` Paolo Bonzini
2020-11-30 10:39       ` David Woodhouse
2020-11-30 11:03         ` Paolo Bonzini
2020-11-30 11:27           ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 02/39] KVM: x86/xen: intercept xen hypercalls if enabled Joao Martins
2019-02-21 18:29   ` Sean Christopherson
2019-02-21 20:56     ` Joao Martins
2019-02-22  0:30       ` Sean Christopherson
2019-02-22 12:50         ` Paolo Bonzini
2020-12-01  9:48   ` David Woodhouse
2020-12-01 11:19     ` David Woodhouse
2020-12-02 11:17       ` Joao Martins
2020-12-02 12:12         ` David Woodhouse
2020-12-02  5:19     ` Ankur Arora
2020-12-02  8:03       ` David Woodhouse
2020-12-02 18:20         ` Ankur Arora
2019-02-20 20:15 ` [PATCH RFC 03/39] KVM: x86/xen: register shared_info page Joao Martins
2020-12-01 13:07   ` David Woodhouse
2020-12-02  0:40     ` Ankur Arora
2020-12-02  1:26       ` David Woodhouse
2020-12-02  5:17         ` Ankur Arora
2020-12-02 10:50           ` Joao Martins
2020-12-02 10:44       ` Joao Martins
2020-12-02 12:20         ` David Woodhouse
2020-12-02 20:32           ` Ankur Arora
2020-12-03 10:16             ` David Woodhouse
2020-12-04 17:30               ` Sean Christopherson
2020-12-02 20:33         ` Ankur Arora
2020-12-12 12:07       ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 04/39] KVM: x86/xen: setup pvclock updates Joao Martins
2019-02-20 20:15 ` [PATCH RFC 05/39] KVM: x86/xen: update wallclock region Joao Martins
2019-02-20 20:15 ` [PATCH RFC 06/39] KVM: x86/xen: register vcpu info Joao Martins
2019-02-20 20:15 ` [PATCH RFC 07/39] KVM: x86/xen: register vcpu time info region Joao Martins
2019-02-20 20:15 ` [PATCH RFC 08/39] KVM: x86/xen: register steal clock Joao Martins
2019-02-20 20:15 ` [PATCH RFC 09/39] KVM: x86: declare Xen HVM guest capability Joao Martins
2019-02-20 20:15 ` [PATCH RFC 10/39] KVM: x86/xen: support upcall vector Joao Martins
2020-12-02 11:17   ` David Woodhouse
2020-12-02 13:12     ` Joao Martins [this message]
2020-12-02 16:47       ` David Woodhouse
2020-12-02 18:34         ` Joao Martins
2020-12-02 19:02           ` David Woodhouse
2020-12-02 20:12             ` Joao Martins
2020-12-02 20:37               ` David Woodhouse
2020-12-03  1:08             ` Ankur Arora
2020-12-08 16:08             ` David Woodhouse
2020-12-09  6:35               ` Ankur Arora
2020-12-09 10:27                 ` David Woodhouse
2020-12-09 10:51                   ` Joao Martins
2020-12-09 11:39                     ` David Woodhouse
2020-12-09 13:26                       ` Joao Martins
2020-12-09 15:41                         ` David Woodhouse
2020-12-09 16:12                           ` Joao Martins
2021-01-01 14:33           ` David Woodhouse
2021-01-05 12:11             ` Joao Martins
2021-01-05 13:23               ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 11/39] KVM: x86/xen: evtchn signaling via eventfd Joao Martins
2020-11-30  9:41   ` David Woodhouse
2020-11-30 12:17     ` Joao Martins
2020-11-30 12:55       ` David Woodhouse
2020-11-30 15:08         ` Joao Martins
2020-11-30 16:48           ` David Woodhouse
2020-11-30 17:15             ` Joao Martins
2020-11-30 18:01               ` David Woodhouse
2020-11-30 18:41                 ` Joao Martins
2020-11-30 19:04                   ` David Woodhouse
2020-11-30 19:25                     ` Joao Martins
2021-11-23 13:15           ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 12/39] KVM: x86/xen: store virq when assigning evtchn Joao Martins
     [not found]   ` <b750291466f3c89e0a393e48079c087704b217a5.camel@amazon.co.uk>
2022-02-10 12:17     ` Joao Martins
2022-02-10 15:23       ` [EXTERNAL] " David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 13/39] KVM: x86/xen: handle PV timers oneshot mode Joao Martins
2019-02-20 20:15 ` [PATCH RFC 14/39] KVM: x86/xen: handle PV IPI vcpu yield Joao Martins
2019-02-20 20:15 ` [PATCH RFC 15/39] KVM: x86/xen: handle PV spinlocks slowpath Joao Martins
2022-02-08 12:36   ` David Woodhouse
2022-02-10 12:17     ` Joao Martins
2022-02-10 14:11       ` David Woodhouse
2019-02-20 20:15 ` [PATCH RFC 16/39] KVM: x86: declare Xen HVM evtchn offload capability Joao Martins
2019-02-20 20:15 ` [PATCH RFC 17/39] x86/xen: export vcpu_info and shared_info Joao Martins
2019-02-20 20:15 ` [PATCH RFC 18/39] x86/xen: make hypercall_page generic Joao Martins
2019-02-20 20:15 ` [PATCH RFC 19/39] xen/xenbus: xenbus uninit support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 20/39] xen-blkback: module_exit support Joao Martins
2019-02-25 18:57   ` Konrad Rzeszutek Wilk
2019-02-26 11:20     ` Joao Martins
2019-02-20 20:15 ` [PATCH RFC 21/39] KVM: x86/xen: domid allocation Joao Martins
2019-02-20 20:15 ` [PATCH RFC 22/39] KVM: x86/xen: grant table init Joao Martins
2019-02-20 20:15 ` [PATCH RFC 23/39] KVM: x86/xen: grant table grow support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 24/39] KVM: x86/xen: backend hypercall support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 25/39] KVM: x86/xen: grant map support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 26/39] KVM: x86/xen: grant unmap support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 27/39] KVM: x86/xen: grant copy support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 28/39] KVM: x86/xen: interdomain evtchn support Joao Martins
2019-02-20 20:15 ` [PATCH RFC 29/39] KVM: x86/xen: evtchn unmask support Joao Martins
2019-02-20 20:16 ` [PATCH RFC 30/39] KVM: x86/xen: add additional evtchn ops Joao Martins
2019-02-20 20:16 ` [PATCH RFC 31/39] xen-shim: introduce shim domain driver Joao Martins
2019-02-20 20:16 ` [PATCH RFC 32/39] xen/balloon: xen_shim_domain() support Joao Martins
2019-02-20 20:16 ` [PATCH RFC 33/39] xen/grant-table: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 34/39] xen/gntdev: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 35/39] xen/xenbus: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 36/39] drivers/xen: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 37/39] xen-netback: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 38/39] xen-blkback: " Joao Martins
2019-02-20 20:16 ` [PATCH RFC 39/39] KVM: x86: declare Xen HVM Dom0 capability Joao Martins
2019-02-20 21:09 ` [PATCH RFC 00/39] x86/KVM: Xen HVM guest support Paolo Bonzini
2019-02-21  0:29   ` Ankur Arora
2019-02-21 11:45   ` Joao Martins
2019-02-22 16:59     ` Paolo Bonzini
2019-03-12 17:14       ` Joao Martins
2019-04-08  6:44         ` Juergen Gross
2019-04-08 10:36           ` Joao Martins
2019-04-08 10:42             ` Juergen Gross
2019-04-08 17:31               ` Joao Martins
2019-04-09  0:35                 ` Stefano Stabellini
2019-04-10  5:50                   ` [Xen-devel] " Ankur Arora
2019-04-10 20:45                     ` Stefano Stabellini
2019-04-09  5:04                 ` Juergen Gross
2019-04-10  6:55                   ` Ankur Arora
2019-04-10  7:14                     ` Juergen Gross
2019-02-20 23:39 ` [Xen-devel] " Marek Marczykowski-Górecki
2019-02-21  0:31   ` Ankur Arora
2019-02-21  7:57   ` Juergen Gross
2019-02-21 12:00     ` Joao Martins
2019-02-21 11:55   ` Joao Martins

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