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From: Ankur Arora <ankur.a.arora@oracle.com>
To: David Woodhouse <dwmw2@infradead.org>,
	Joao Martins <joao.m.martins@oracle.com>,
	karahmed@amazon.de
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: Tue, 8 Dec 2020 22:35:45 -0800	[thread overview]
Message-ID: <1af00fa4-03b8-a059-d859-5cfd71ef10f4@oracle.com> (raw)
In-Reply-To: <6a6b5806be1fe4c0fe96c0b664710d1ce614f29d.camel@infradead.org>

On 2020-12-08 8:08 a.m., David Woodhouse wrote:
> On Wed, 2020-12-02 at 19:02 +0000, David Woodhouse wrote:
>>
>>> I feel we could just accommodate it as subtype in KVM_XEN_ATTR_TYPE_CALLBACK_VIA.
>>> Don't see the adavantage in having another xen attr type.
>>
>> Yeah, fair enough.
>>
>>> But kinda have mixed feelings in having kernel handling all event channels ABI,
>>> as opposed to only the ones userspace asked to offload. It looks a tad unncessary besides
>>> the added gain to VMMs that don't need to care about how the internals of event channels.
>>> But performance-wise it wouldn't bring anything better. But maybe, the former is reason
>>> enough to consider it.
>>
>> Yeah, we'll see. Especially when it comes to implementing FIFO event
>> channels, I'd rather just do it in one place — and if the kernel does
>> it anyway then it's hardly difficult to hook into that.
>>
>> But I've been about as coherent as I can be in email, and I think we're
>> generally aligned on the direction. I'll do some more experiments and
>> see what I can get working, and what it looks like.
> 
> 
> So... I did some more typing, and revived our completely userspace
> based implementation of event channels. I wanted to declare that such
> was *possible*, and that using the kernel for IPI and VIRQ was just a
> very desirable optimisation.
> 
> It looks like Linux doesn't use the per-vCPU upcall vector that you
> called 'KVM_XEN_CALLBACK_VIA_EVTCHN'. So I'm delivering interrupts via
> KVM_INTERRUPT as if they were ExtINT....
> 
> ... except I'm not. Because the kernel really does expect that to be an
> ExtINT from a legacy PIC, and kvm_apic_accept_pic_intr() only returns
> true if LVT0 is set up for EXTINT and unmasked.
> 
> I messed around with this hack and increasingly desperate variations on
> the theme (since this one doesn't cause the IRQ window to be opened to
> userspace in the first place), but couldn't get anything working:

Increasingly desperate variations,  about sums up my process as well while
trying to get the upcall vector working.

> 
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2380,6 +2380,9 @@ int kvm_apic_accept_pic_intr(struct kvm_vcpu *vcpu)
>          if ((lvt0 & APIC_LVT_MASKED) == 0 &&
>              GET_APIC_DELIVERY_MODE(lvt0) == APIC_MODE_EXTINT)
>                  r = 1;
> +       /* Shoot me. */
> +       if (vcpu->arch.pending_external_vector == 243)
> +               r = 1;
>          return r;
>   }
>   
> 
> Eventually I resorted to delivering the interrupt through the lapic
> *anyway* (through KVM_SIGNAL_MSI with an MSI message constructed for
> the appropriate vCPU/vector) and the following hack to auto-EOI:
> 
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2416,7 +2419,7 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
>           */
>   
>          apic_clear_irr(vector, apic);
> -       if (test_bit(vector, vcpu_to_synic(vcpu)->auto_eoi_bitmap)) {
> +       if (vector == 243 || test_bit(vector, vcpu_to_synic(vcpu)->auto_eoi_bitmap)) {
>                  /*
>                   * For auto-EOI interrupts, there might be another pending
>                   * interrupt above PPR, so check whether to raise another
> 
> 
> That works, and now my guest finishes the SMP bringup (and gets as far
> as waiting on the XenStore implementation that I haven't put back yet).
> 
> So I think we need at least a tiny amount of support in-kernel for
> delivering event channel interrupt vectors, even if we wanted to allow
> for a completely userspace implementation.
> 
> Unless I'm missing something?

I did use the auto_eoi hack as well. So, yeah, I don't see any way of
getting around this.

Also, IIRC we had eventually gotten rid of the auto_eoi approach
because that wouldn't work with APICv. At that point we resorted to
direct queuing for vectored callbacks which was a hack that I never
grew fond of...
  
> I will get on with implementing the in-kernel handling with IRQ routing
> entries targeting a given { port, vcpu }. And I'm kind of vacillating
> about whether the mode/vector should be separately configured, or
> whether they might as well be in the IRQ routing table too, even if
> it's kind of redundant because it's specified the same for *every* port
> targeting the same vCPU. I *think* I prefer that redundancy over having
> a separate configuration mechanism to set the vector for each vCPU. But
> we'll see what happens when my fingers do the typing...
> 

Good luck to your fingers!

Ankur

  reply	other threads:[~2020-12-09  6:36 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
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 [this message]
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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