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

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Date:   Wed, 14 Dec 2016 13:39:05 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Igor Mammedov <imammedo@...hat.com>
Subject: Re: [PATCH v2 2/4] KVM: x86: replace kvm_apic_id with
 kvm_{x,x2}apic_id

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.

Can you elaborate?


-- 

David