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From: Paolo Bonzini <pbonzini@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Andrew Honig <ahonig@google.com>,
	linux-kernel@vger.kernel.org, kvm <kvm@vger.kernel.org>,
	"Lan, Tianyu" <tianyu.lan@intel.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Jan Kiszka <jan.kiszka@web.de>, Peter Xu <peterx@redhat.com>
Subject: Re: [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map
Date: Fri, 1 Jul 2016 17:06:23 +0200	[thread overview]
Message-ID: <a0bf56bd-48dd-a469-ca62-e36ec3ed72d8@redhat.com> (raw)
In-Reply-To: <20160701143827.GE27840@potion>



On 01/07/2016 16:38, Radim Krčmář wrote:
>> > Should it?
> Yes, x2APIC ID cannot be changed in hardware and is initialized to the
> intitial APIC ID.
> Letting LAPIC_SET change x2APIC ID would allow scenarios where userspace
> reuses old VMs instead of building new ones after reconfiguration.
> I don't think it's a sensible use case and it it is currently broken,
> because we don't exit to userspace when changing APIC mode, so KVM would
> just set APIC ID to VCPU ID on any transition and userspace couldn't
> amend it.
> 
>> >             According to QEMU if you have e.g. 3 cores per socket one
>> > socket take 4 APIC IDs.  For Knights Landing the "worst" prime factor in
>> > 288 is 3^2 so you need APIC IDs up to 288 * (4/3)^2 = 512.
> The topology can result in sparse APIC ID and APIC ID is initialized
> from VCPU ID, so userspace has to pick VCPU ID accordingly.

Right, I was confusing KVM_MAX_VCPUS and KVM_MAX_VCPU_ID.  So the
overflow case cannot happen and neither can the 32GB allocation.  On the
other hand, I suspect you need to bump KVM_MAX_VCPU_ID beyond its
current default setting (which is equal to KVM_MAX_VCPUS), up to 511 or
1023.

Thanks,

Paolo

  reply	other threads:[~2016-07-01 15:06 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-30 20:54 [PATCH v1 00/11] KVM: x86: break the xAPIC barrier Radim Krčmář
2016-06-30 20:54 ` [PATCH v1 01/11] KVM: x86: bump KVM_SOFT_MAX_VCPUS to 240 Radim Krčmář
2016-07-01  8:42   ` Paolo Bonzini
2016-06-30 20:54 ` [PATCH v1 02/11] KVM: x86: add kvm_apic_map_get_dest_lapic Radim Krčmář
2016-07-01  7:57   ` Paolo Bonzini
2016-07-01 12:39     ` Radim Krčmář
2016-06-30 20:54 ` [PATCH v1 03/11] KVM: x86: dynamic kvm_apic_map Radim Krčmář
2016-06-30 22:15   ` Andrew Honig
2016-07-01  8:42     ` Paolo Bonzini
2016-07-01 12:44       ` Radim Krčmář
2016-07-01 14:03         ` Paolo Bonzini
2016-07-01 14:38           ` Radim Krčmář
2016-07-01 15:06             ` Paolo Bonzini [this message]
2016-07-01 15:12               ` Paolo Bonzini
2016-07-01 15:43                 ` Radim Krčmář
2016-07-01 16:38                   ` Paolo Bonzini
2016-07-01 15:35               ` Radim Krčmář
2016-07-01  7:33   ` Paolo Bonzini
2016-06-30 20:54 ` [PATCH v1 04/11] KVM: x86: use u16 for logical VCPU mask in lapic Radim Krčmář
2016-07-01  7:56   ` Paolo Bonzini
2016-07-01 12:48     ` Radim Krčmář
2016-07-01 14:04       ` Paolo Bonzini
2016-06-30 20:54 ` [PATCH v1 05/11] KVM: x86: use generic function for MSI parsing Radim Krčmář
2016-07-01  8:42   ` Paolo Bonzini
2016-06-30 20:54 ` [PATCH v1 06/11] KVM: x86: use hardware-compatible format for APIC ID register Radim Krčmář
2016-07-01  8:33   ` Paolo Bonzini
2016-07-01 13:11     ` Radim Krčmář
2016-07-01 14:12       ` Paolo Bonzini
2016-07-01 14:54         ` Radim Krčmář
2016-07-01 15:07           ` Paolo Bonzini
2016-07-01 15:53             ` Radim Krčmář
2016-07-01 16:37               ` Paolo Bonzini
2016-06-30 20:54 ` [PATCH v1 07/11] KVM: VMX: optimize APIC ID read with APICv Radim Krčmář
2016-07-01  8:42   ` Paolo Bonzini
2016-06-30 20:54 ` [PATCH v1 08/11] KVM: x86: directly call recalculate_apic_map on lapic restore Radim Krčmář
2016-07-01  8:43   ` Paolo Bonzini
2016-06-30 20:54 ` [PATCH v1 09/11] KVM: x86: reset lapic base in kvm_lapic_reset Radim Krčmář
2016-07-01  8:43   ` Paolo Bonzini
2016-06-30 20:54 ` [PATCH v1 10/11] KVM: x86: add KVM_CAP_X2APIC_API Radim Krčmář
2016-07-01  8:24   ` Paolo Bonzini
2016-07-01 13:25     ` Radim Krčmář
2016-07-01 18:09   ` David Matlack
2016-07-01 18:31     ` Radim Krčmář
2016-06-30 20:54 ` [PATCH v1 11/11] KVM: x86: bump MAX_VCPUS to 288 Radim Krčmář
2016-07-01  8:43   ` Paolo Bonzini

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