linux-kernel - Re: [PATCH v2 2/4] KVM: x86: replace kvm_apic_id with kvm_{x,x2}apic

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Message-ID: <e2d692e5-a711-cacc-ef79-23e388953cd7@redhat.com>
Date:   Wed, 14 Dec 2016 16:50:34 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Igor Mammedov <imammedo@...hat.com>
Subject: Re: [PATCH v2 2/4] KVM: x86: replace kvm_apic_id with
 kvm_{x,x2}apic_id



On 14/12/2016 14:41, Radim Krčmář wrote:
> 2016-12-14 13:39+0100, David Hildenbrand:
>> Am 13.12.2016 um 17:29 schrieb Radim Krčmář:
>>> There were three calls sites:
>>>  - recalculate_apic_map and kvm_apic_match_physical_addr, where it would
>>>    only complicate implementation of x2APIC hotplug;
>>>  - in apic_debug, where it was still somewhat preserved, but keeping the
>>>    old function just for apic_debug was not worth it
>>>
>>> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
>>> ---
>>>  arch/x86/kvm/lapic.c | 41 ++++++++++++++++++++++++++++++-----------
>>>  arch/x86/kvm/lapic.h | 11 -----------
>>>  2 files changed, 30 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>>> index 09edd32b8e42..e645b4bc6437 100644
>>> --- a/arch/x86/kvm/lapic.c
>>> +++ b/arch/x86/kvm/lapic.c
>>> @@ -115,6 +115,16 @@ static inline int apic_enabled(struct kvm_lapic *apic)
>>>  	(LVT_MASK | APIC_MODE_MASK | APIC_INPUT_POLARITY | \
>>>  	 APIC_LVT_REMOTE_IRR | APIC_LVT_LEVEL_TRIGGER)
>>>
>>> +static inline u8 kvm_xapic_id(struct kvm_lapic *apic)
>>> +{
>>> +	return kvm_lapic_get_reg(apic, APIC_ID) >> 24;
>>> +}
>>> +
>>> +static inline u32 kvm_x2apic_id(struct kvm_lapic *apic)
>>> +{
>>> +	return apic->vcpu->vcpu_id;
>>> +}
>>> +
>>>  static inline bool kvm_apic_map_get_logical_dest(struct kvm_apic_map *map,
>>>  		u32 dest_id, struct kvm_lapic ***cluster, u16 *mask) {
>>>  	switch (map->mode) {
>>> @@ -159,13 +169,13 @@ static void recalculate_apic_map(struct kvm *kvm)
>>>  	struct kvm_apic_map *new, *old = NULL;
>>>  	struct kvm_vcpu *vcpu;
>>>  	int i;
>>> -	u32 max_id = 255;
>>> +	u32 max_id = 256; /* enough space for any xAPIC ID */
>>
>> Why exactly do we have to increase this?
>>
>> I thought the maximum xapic id is 255, and we correctly allocate
>> 255+1 slots.
>>
>> Now, we would allocate 257 slots and set max_apic_id to 256.
> 
> Right, it is a typical off-by-one error.  The comment is sufficient ...

I can change it myself too.

Paolo