[PATCH v5 16/22] KVM: arm64: vgic-its: Add infrastructure for table lookup

[Christoffer Dall]

On Fri, Apr 14, 2017 at 12:15:28PM +0200, Eric Auger wrote:
> Add a generic lookup_table() helper whose role consists in
> scanning a contiguous table located in guest RAM and applying
> a callback on each entry. Entries can be handled as linked lists
> since the callback may return an offset to the next entry and
> also tell that an entry is the last one.
> 
> Helper functions also are added to compute the device/event ID
> offset to the next DTE/ITE.
> 
> compute_next_devid_offset, compute_next_eventid_offset and
> lookup_table will become static in subsequent patches
> 
> Signed-off-by: Eric Auger <eric.auger at redhat.com>
> 
> ---
> v4 -> v5:
> - use kvm_read_guest
> 
> v3 -> v4:
> - remove static to avoid compilation warning
> - correct size computation in looup_table()
> - defines now encode the number of bits used for devid and eventid offsets
> - use BIT() - 1 to encode the max offets
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 93 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 93 insertions(+)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 56c5123..c22b35d 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -195,6 +195,8 @@ static struct its_ite *find_ite(struct vgic_its *its, u32 device_id,
>  
>  #define VITS_TYPER_IDBITS 16
>  #define VITS_TYPER_DEVBITS 16
> +#define VITS_DTE_MAX_DEVID_OFFSET	(BIT(14) - 1)
> +#define VITS_ITE_MAX_EVENTID_OFFSET	(BIT(16) - 1)
>  
>  /*
>   * Finds and returns a collection in the ITS collection table.
> @@ -1674,6 +1676,97 @@ int vgic_its_attr_regs_access(struct kvm_device *dev,
>  	return ret;
>  }
>  
> +u32 compute_next_devid_offset(struct list_head *h, struct its_device *dev)
> +{
> +	struct list_head *e = &dev->dev_list;
> +	struct its_device *next;
> +	u32 next_offset;
> +
> +	if (e->next == h)
> +		return 0;
> +	next = list_entry(e->next, struct its_device, dev_list);
> +	next_offset = next->device_id - dev->device_id;
> +
> +	return min_t(u32, next_offset, VITS_DTE_MAX_DEVID_OFFSET);
> +}
> +
> +u32 compute_next_eventid_offset(struct list_head *h, struct its_ite *ite)
> +{
> +	struct list_head *e = &ite->ite_list;
> +	struct its_ite *next;
> +	u32 next_offset;
> +
> +	if (e->next == h)
> +		return 0;
> +	next = list_entry(e->next, struct its_ite, ite_list);
> +	next_offset = next->event_id - ite->event_id;
> +
> +	return min_t(u32, next_offset, VITS_ITE_MAX_EVENTID_OFFSET);

nit: in both of these functions you can avoid the extra e variable and
maybe make this slightly more readable by using these two calls instead:

list_is_last(&ite->ite_list, h);
next = list_next_entry(ite, ite_list);

Thanks,
-Christoffer