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From: David Woodhouse <dwmw2@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>,
	x86@kernel.org, Marc Zyngier <maz@kernel.org>
Cc: kvm <kvm@vger.kernel.org>, Paolo Bonzini <pbonzini@redhat.com>,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/5] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST_ID
Date: Tue, 13 Oct 2020 12:51:00 +0100
Message-ID: <0ca196c0df5beb90b45457ac7ca5d8611d2a7a29.camel@infradead.org> (raw)
In-Reply-To: <832c2d4c11cd99382782474f51d15889ffa24407.camel@infradead.org>


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On Tue, 2020-10-13 at 11:53 +0100, David Woodhouse wrote:
> On Tue, 2020-10-13 at 12:46 +0200, Thomas Gleixner wrote:
> > And after becoming more awake, that wont work anyway because there is
> > more than one IR domain, so there is no way to return an error "You
> > forgot to register" obviously.
> > 
> > But the APIC id (32768) valid check is also broken because IR can be
> > enabled even without X2APIC.
> 
> Nope, it's perfectly OK to allow HPET and I/OAPIC to be parented in the
> x86_vector_domain in that case, regardless of IR.
> 
> The *actual* criterion for x86_vector_select() returning zero to say 
> "don't use me" is "could there be CPUs in the system which can't be
> reached through x86_vector_msi_compose_msg()?". It's not really about
> IR at all.
> 
> The apic_id_valid(32768) check is checking precisely the right thing.

With that realisation, I've fixed the comment in my ext_dest_id branch
to remove all mention of IRQ remapping. It now looks like this:

static int x86_vector_select(struct irq_domain *d, struct irq_fwspec *fwspec,
			     enum irq_domain_bus_token bus_token)
{
	/*
	 * HPET and I/OAPIC drivers use irq_find_matching_irqdomain()
	 * to find their parent irqdomain. For x86_vector_domain to be
	 * suitable, all CPUs in the system must be reachable by its
	 * x86_vector_msi_compose_msg() function. Which is only true
	 * in !x2apic mode, or in x2apic physical mode if APIC IDs were
	 * restricted to 8 or 15 bits at boot time. In those cases,
	 * 1<<15 will *not* be a valid APIC ID.
	 */
	if (apic->apic_id_valid(1<<15))
		return 0;

	return x86_fwspec_is_ioapic(fwspec) || x86_fwspec_is_hpet(fwspec);
}

That makes it clearer that this isn't just some incestuous interaction
with IRQ remapping — that APIC ID limit really is the basis on which
this irqdomain, all by itself, makes the decision about whether it's
capable of being the parent irqdomain to the requesting device.

It just so happens that *if* you allow higher APIC IDs in the system
and *if* no other irqdomains exist which take ownership of a given HPET
or I/OAPIC, then that child device will fail to find a suitable parent
irqdomain and will fail to initialise. And that's just how we want it.

Sure, we have that special case in x2apic startup where we ensure that
if we don't have IR then we limit the APIC IDs. But that's there, and
*this* code is perfectly self-contained and isolated.

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  reply index

Thread overview: 113+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-07 12:20 [PATCH 0/5] Fix x2apic enablement and allow up to 32768 CPUs without IR where supported David Woodhouse
2020-10-07 12:20 ` [PATCH 1/5] x86/apic: Fix x2apic enablement without interrupt remapping David Woodhouse
2020-10-07 12:20   ` [PATCH 2/5] x86/msi: Only use high bits of MSI address for DMAR unit David Woodhouse
2020-10-07 12:20   ` [PATCH 3/5] x86/ioapic: Handle Extended Destination ID field in RTE David Woodhouse
2020-10-08  9:12     ` Peter Zijlstra
2020-10-08 17:05       ` David Woodhouse
2020-10-08 11:41     ` Thomas Gleixner
2020-10-07 12:20   ` [PATCH 4/5] x86/apic: Support 15 bits of APIC ID in IOAPIC/MSI where available David Woodhouse
2020-10-08 11:54     ` Thomas Gleixner
2020-10-08 12:02       ` Thomas Gleixner
2020-10-08 13:00       ` David Woodhouse
2020-10-07 12:20   ` [PATCH 5/5] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST_ID David Woodhouse
2020-10-08 12:05     ` Thomas Gleixner
2020-10-08 12:55       ` David Woodhouse
2020-10-08 16:08         ` David Woodhouse
2020-10-08 21:14           ` Thomas Gleixner
2020-10-08 21:39             ` David Woodhouse
2020-10-08 23:27               ` Thomas Gleixner
2020-10-09  6:07                 ` David Woodhouse
2020-10-10 10:06                 ` David Woodhouse
2020-10-10 11:44                   ` Thomas Gleixner
2020-10-10 11:58                     ` David Woodhouse
2020-10-11 17:12                       ` Thomas Gleixner
2020-10-11 21:15                         ` David Woodhouse
2020-10-12  9:33                           ` Thomas Gleixner
2020-10-12 16:06                             ` David Woodhouse
2020-10-12 18:38                               ` Thomas Gleixner
2020-10-12 20:20                                 ` David Woodhouse
2020-10-12 22:13                                   ` Thomas Gleixner
2020-10-13  7:52                                     ` David Woodhouse
2020-10-13  8:11                                       ` [PATCH 0/9] Remove irq_remapping_get_irq_domain() David Woodhouse
2020-10-13  8:11                                         ` [PATCH 1/9] genirq/irqdomain: Implement get_name() method on irqchip fwnodes David Woodhouse
2020-10-13  8:11                                         ` [PATCH 2/9] x86/apic: Add select() method on vector irqdomain David Woodhouse
2020-10-13  8:11                                         ` [PATCH 3/9] iommu/amd: Implement select() method on remapping irqdomain David Woodhouse
2020-10-13  8:11                                         ` [PATCH 4/9] iommu/vt-d: " David Woodhouse
2020-10-13  8:11                                         ` [PATCH 5/9] iommu/hyper-v: " David Woodhouse
2020-10-13  8:11                                         ` [PATCH 6/9] x86/hpet: Use irq_find_matching_fwspec() to find " David Woodhouse
2020-10-13  8:11                                         ` [PATCH 7/9] x86/ioapic: " David Woodhouse
2020-10-13  8:11                                         ` [PATCH 8/9] x86: Kill all traces of irq_remapping_get_irq_domain() David Woodhouse
2020-10-13  8:11                                         ` [PATCH 9/9] iommu/vt-d: Simplify intel_irq_remapping_select() David Woodhouse
2020-10-13  9:28                                       ` [PATCH 5/5] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST_ID Thomas Gleixner
2020-10-13 10:15                                         ` David Woodhouse
2020-10-13 10:46                                         ` Thomas Gleixner
2020-10-13 10:53                                           ` David Woodhouse
2020-10-13 11:51                                             ` David Woodhouse [this message]
2020-10-13 12:40                                               ` Thomas Gleixner
2020-10-08 11:46   ` [PATCH 1/5] x86/apic: Fix x2apic enablement without interrupt remapping Thomas Gleixner
2020-10-09 10:46 ` [PATCH v2 0/8] Fix x2apic enablement and allow up to 32768 CPUs without IR where supported David Woodhouse
2020-10-09 10:46   ` [PATCH v2 1/8] x86/apic: Fix x2apic enablement without interrupt remapping David Woodhouse
2020-10-09 10:46   ` [PATCH v2 2/8] x86/msi: Only use high bits of MSI address for DMAR unit David Woodhouse
2020-10-09 10:46   ` [PATCH v2 3/8] x86/apic: Always provide irq_compose_msi_msg() method for vector domain David Woodhouse
2020-10-09 10:46   ` [PATCH v2 4/8] x86/ioapic: Handle Extended Destination ID field in RTE David Woodhouse
2020-10-09 10:46   ` [PATCH v2 5/8] x86/apic: Support 15 bits of APIC ID in MSI where available David Woodhouse
2020-10-09 10:46   ` [PATCH v2 6/8] x86/kvm: Add KVM_FEATURE_MSI_EXT_DEST_ID David Woodhouse
2020-10-09 10:46   ` [PATCH v2 7/8] x86/hpet: Move MSI support into hpet.c David Woodhouse
2020-10-09 10:46   ` [PATCH v2 8/8] x86/ioapic: Generate RTE directly from parent irqchip's MSI message David Woodhouse
2020-10-22 21:43     ` Thomas Gleixner
2020-10-22 22:10       ` Thomas Gleixner
2020-10-23 17:04         ` David Woodhouse
2020-10-23 10:10       ` David Woodhouse
2020-10-23 21:28         ` Thomas Gleixner
2020-10-24  8:26           ` David Woodhouse
2020-10-24  8:41             ` David Woodhouse
2020-10-24  9:13             ` Paolo Bonzini
2020-10-24 10:13               ` David Woodhouse
2020-10-24 12:44                 ` David Woodhouse
2020-10-24 21:35                   ` [PATCH v3 00/35] Fix x2apic enablement and allow more CPUs, clean up I/OAPIC and MSI bitfields David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 01/35] x86/apic: Fix x2apic enablement without interrupt remapping David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 02/35] x86/msi: Only use high bits of MSI address for DMAR unit David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 03/35] x86/apic/uv: Fix inconsistent destination mode David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 04/35] x86/devicetree: Fix the ioapic interrupt type table David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 05/35] x86/apic: Cleanup delivery mode defines David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 06/35] x86/apic: Replace pointless apic::dest_logical usage David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 07/35] x86/apic: Get rid of apic::dest_logical David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 08/35] x86/apic: Cleanup destination mode David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 09/35] x86/apic: Always provide irq_compose_msi_msg() method for vector domain David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 10/35] x86/hpet: Move MSI support into hpet.c David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 11/35] genirq/msi: Allow shadow declarations of msi_msg::$member David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 12/35] x86/msi: Provide msi message shadow structs David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 13/35] iommu/intel: Use msi_msg " David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 14/35] iommu/amd: " David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 15/35] PCI: vmd: " David Woodhouse
2020-10-28 20:49                       ` Kees Cook
2020-10-28 21:13                         ` Thomas Gleixner
2020-10-28 23:22                           ` Kees Cook
2020-10-24 21:35                     ` [PATCH v3 16/35] x86/kvm: " David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 17/35] x86/pci/xen: " David Woodhouse
2020-10-25  9:49                       ` David Laight
2020-10-25 10:26                         ` David Woodhouse
2020-10-25 13:20                           ` David Laight
2020-10-24 21:35                     ` [PATCH v3 18/35] x86/msi: Remove msidef.h David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 19/35] x86/io_apic: Cleanup trigger/polarity helpers David Woodhouse
2020-11-10  6:31                       ` Qian Cai
2020-11-10  8:59                         ` David Woodhouse
2020-11-10 16:26                           ` Paolo Bonzini
2020-10-24 21:35                     ` [PATCH v3 20/35] x86/ioapic: Cleanup IO/APIC route entry structs David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 21/35] x86/ioapic: Generate RTE directly from parent irqchip's MSI message David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 22/35] genirq/irqdomain: Implement get_name() method on irqchip fwnodes David Woodhouse
2020-10-25  9:41                       ` Marc Zyngier
2020-10-24 21:35                     ` [PATCH v3 23/35] x86/apic: Add select() method on vector irqdomain David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 24/35] iommu/amd: Implement select() method on remapping irqdomain David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 25/35] iommu/vt-d: " David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 26/35] iommu/hyper-v: " David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 27/35] x86/hpet: Use irq_find_matching_fwspec() to find " David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 28/35] x86/ioapic: " David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 29/35] x86: Kill all traces of irq_remapping_get_irq_domain() David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 30/35] iommu/vt-d: Simplify intel_irq_remapping_select() David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 31/35] x86/ioapic: Handle Extended Destination ID field in RTE David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 32/35] x86/apic: Support 15 bits of APIC ID in MSI where available David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 33/35] iommu/hyper-v: Disable IRQ pseudo-remapping if 15 bit APIC IDs are available David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 34/35] x86/kvm: Reserve KVM_FEATURE_MSI_EXT_DEST_ID David Woodhouse
2020-10-24 21:35                     ` [PATCH v3 35/35] x86/kvm: Enable 15-bit extension when KVM_FEATURE_MSI_EXT_DEST_ID detected David Woodhouse
2020-10-25  8:12                     ` [PATCH v3 00/35] Fix x2apic enablement and allow more CPUs, clean up I/OAPIC and MSI bitfields David Woodhouse

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