linux-kernel - Re: [PATCH v3 04/14] KVM: x86: dynamic kvm_apic

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Message-ID: <20160802122207.GC3758@potion>
Date:	Tue, 2 Aug 2016 14:22:07 +0200
From:	Radim Krčmář <rkrcmar@...hat.com>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
	"Lan, Tianyu" <tianyu.lan@...el.com>,
	Igor Mammedov <imammedo@...hat.com>,
	Jan Kiszka <jan.kiszka@....de>, Peter Xu <peterx@...hat.com>,
	Yang Zhang <yang.zhang.wz@...il.com>
Subject: Re: [PATCH v3 04/14] KVM: x86: dynamic kvm_apic_map

2016-08-02 19:39+0800, Wanpeng Li:
> 2016-07-13 4:09 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> [...]
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> @@ -152,14 +152,22 @@ static void recalculate_apic_map(struct kvm *kvm)
>>         struct kvm_apic_map *new, *old = NULL;
>>         struct kvm_vcpu *vcpu;
>>         int i;
>> -
>> -       new = kzalloc(sizeof(struct kvm_apic_map), GFP_KERNEL);
>> +       u32 max_id = 255;
> 
> If this should be max_id = KVM_MAX_VCPU_ID? I have a patch on hand to
> fix it, but I didn't know whether it is your desired behavior or not.

No, we could just have static array then.  KVM_MAX_VCPU_ID is expected
to be raised to INT_MAX and eventually UINT_MAX, so it would not be
practical.  The dynamic array is there to avoid wasting space in the
common case, where VMs have only low APIC IDs.

Inintial patches had 255 to minimize a chance of regressions as the
static array was that big, but starting with max_id = 0 is our goal and
should be ok even without other changes.