Re: [PATCH 8/8] KVM: x86: simplify kvm_apic_map

[Paolo Bonzini <pbonzini@redhat.com>]

On 29/01/2015 22:48, Radim Krčmář wrote:
> recalculate_apic_map() uses two passes over all VCPUs.  This is a relic
> from time when we selected a global mode in the first pass and set up
> the optimized table in the second pass (to have a consistent mode).
> 
> Recent changes made mixed mode unoptimized and we can do it in one pass.
> Format of logical MDA is a function of the mode, so we encode it in
> apic_logical_id() and drop obsoleted variables from the struct.
> 
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  3 --
>  arch/x86/kvm/lapic.c            | 78 ++++++++++-------------------------------
>  arch/x86/kvm/lapic.h            | 29 ++++++++-------
>  3 files changed, 36 insertions(+), 74 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index fec3188cabbb..14b6b0fd17b1 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -555,9 +555,6 @@ struct kvm_arch_memory_slot {
>  struct kvm_apic_map {
>  	struct rcu_head rcu;
>  	u8 mode;
> -	u8 ldr_bits;
> -	/* fields bellow are used to decode ldr values in different modes */
> -	u32 cid_shift, cid_mask, lid_mask;
>  	struct kvm_lapic *phys_map[256];
>  	/* first index is cluster id second is cpu id in a cluster */
>  	struct kvm_lapic *logical_map[16][16];
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 621d9df6ac63..f74557791a77 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -146,49 +146,6 @@ static void recalculate_apic_map(struct kvm *kvm)
>  	if (!new)
>  		goto out;
>  
> -	new->ldr_bits = 8;
> -	/* flat mode is default */
> -	new->cid_shift = 8;
> -	new->cid_mask = 0;
> -	new->lid_mask = 0xff;
> -
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		struct kvm_lapic *apic = vcpu->arch.apic;
> -
> -		if (!kvm_apic_present(vcpu))
> -			continue;
> -
> -		if (apic_x2apic_mode(apic)) {
> -			new->ldr_bits = 32;
> -			new->cid_shift = 16;
> -			new->cid_mask = new->lid_mask = 0xffff;
> -			new->mode |= KVM_APIC_MODE_X2APIC;
> -		} else if (kvm_apic_get_reg(apic, APIC_LDR)) {
> -			if (kvm_apic_get_reg(apic, APIC_DFR) ==
> -							APIC_DFR_CLUSTER) {
> -				new->cid_shift = 4;
> -				new->cid_mask = 0xf;
> -				new->lid_mask = 0xf;
> -				new->mode |= KVM_APIC_MODE_XAPIC_CLUSTER;
> -			} else {
> -				new->cid_shift = 8;
> -				new->cid_mask = 0;
> -				new->lid_mask = 0xff;
> -				new->mode |= KVM_APIC_MODE_XAPIC_FLAT;
> -			}
> -		}
> -
> -		/*
> -		 * All APICs have to be configured in the same mode by an OS.
> -		 * We take advatage of this while building logical id loockup
> -		 * table. After reset APICs are in software disabled mode, so if
> -		 * we find apic with different setting we assume this is the mode
> -		 * OS wants all apics to be in; build lookup table accordingly.
> -		 */
> -		if (kvm_apic_sw_enabled(apic))
> -			break;
> -	}
> -
>  	kvm_for_each_vcpu(i, vcpu, kvm) {
>  		struct kvm_lapic *apic = vcpu->arch.apic;
>  		u16 cid, lid;
> @@ -198,17 +155,22 @@ static void recalculate_apic_map(struct kvm *kvm)
>  			continue;
>  
>  		aid = kvm_apic_id(apic);
> -		ldr = kvm_apic_get_reg(apic, APIC_LDR);
> -		cid = apic_cluster_id(new, ldr);
> -		lid = apic_logical_id(new, ldr);
> -
>  		if (aid < ARRAY_SIZE(new->phys_map))
>  			new->phys_map[aid] = apic;
>  
> -		/* The logical map is definitely wrong if we have multiple
> -		 * modes at the same time.  Physical is still right though.
> -		 */
> -		if (hweight8(new->mode) != 1)
> +		ldr = kvm_apic_get_reg(apic, APIC_LDR);
> +
> +		if (apic_x2apic_mode(apic)) {
> +			new->mode |= KVM_APIC_MODE_X2APIC;
> +		} else if (ldr) {
> +			ldr = GET_APIC_LOGICAL_ID(ldr);
> +			if (kvm_apic_get_reg(apic, APIC_DFR) == APIC_DFR_FLAT)
> +				new->mode |= KVM_APIC_MODE_XAPIC_FLAT;
> +			else
> +				new->mode |= KVM_APIC_MODE_XAPIC_CLUSTER;
> +		}
> +
> +		if (!apic_logical_id(new, ldr, &cid, &lid))
>  			continue;
>  
>  		if (lid && cid < ARRAY_SIZE(new->logical_map))
> @@ -724,22 +686,20 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,
>  
>  		dst = &map->phys_map[irq->dest_id];
>  	} else {
> -		u32 mda = irq->dest_id << (32 - map->ldr_bits);
> -		u16 cid = apic_cluster_id(map, mda);
> +		u16 cid;
>  
> -		if (cid >= ARRAY_SIZE(map->logical_map))
> -			goto out;
> -
> -		if (hweight8(map->mode) != 1) {
> +		if (!apic_logical_id(map, irq->dest_id, &cid, (u16 *)&bitmap))
> +		{
>  			/* Not deliverable with optimized map. */
>  			ret = false;
>  			goto out;
>  		}
>  
> +		if (cid >= ARRAY_SIZE(map->logical_map))
> +			goto out;
> +
>  		dst = map->logical_map[cid];
>  
> -		bitmap = apic_logical_id(map, mda);
> -
>  		if (irq->delivery_mode == APIC_DM_LOWEST) {
>  			int l = -1;
>  			for_each_set_bit(i, &bitmap, 16) {
> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
> index fd0197a93862..320716e301a8 100644
> --- a/arch/x86/kvm/lapic.h
> +++ b/arch/x86/kvm/lapic.h
> @@ -151,19 +151,24 @@ static inline bool kvm_apic_vid_enabled(struct kvm *kvm)
>  	return kvm_x86_ops->vm_has_apicv(kvm);
>  }
>  
> -static inline u16 apic_cluster_id(struct kvm_apic_map *map, u32 ldr)
> +static inline bool
> +apic_logical_id(struct kvm_apic_map *map, u32 ldr, u16 *cid, u16 *lid)
>  {
> -	u16 cid;
> -	ldr >>= 32 - map->ldr_bits;
> -	cid = (ldr >> map->cid_shift) & map->cid_mask;
> -
> -	return cid;
> -}
> -
> -static inline u16 apic_logical_id(struct kvm_apic_map *map, u32 ldr)
> -{
> -	ldr >>= (32 - map->ldr_bits);
> -	return ldr & map->lid_mask;
> +	switch (map->mode) {
> +	case KVM_APIC_MODE_XAPIC_FLAT:
> +		*cid = 0;
> +		*lid = ldr & 0xff;
> +		return true;
> +	case KVM_APIC_MODE_XAPIC_CLUSTER:
> +		*cid = (ldr >> 4) & 0xf;
> +		*lid = ldr & 0xf;
> +		return true;
> +	case KVM_APIC_MODE_X2APIC:
> +		*cid = ldr >> 16;
> +		*lid = ldr & 0xffff;
> +		return true;
> +	}

We need some optimization here.  You can make the defines equal to the
size of the lid: CLUSTER = 1 << 3, FLAT = 1 << 2, X2APIC = 1 << 4:

	BUILD_BUG_ON(...FLAT != 4);
	BUILD_BUG_ON(...CLUSTER != 8);
	BUILD_BUG_ON(...X2APIC != 16);

	lid_bits = mode;
	cid_bits = mode & (16 | 4);
	lid_mask = (1 << lid_bits) - 1;
	cid_mask = (1 << cid_bits) - 1;

	*cid = (ldr >> lid_bits) & cid_mask;
	*lid = ldr & lid_mask;

Please move this to lapic.c since you are at it.

Paolo

> +	return false;
>  }
>  
>  static inline bool kvm_apic_has_events(struct kvm_vcpu *vcpu)
>