[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);
> +}
> +
> +/**
> + * entry_fn_t - Callback called on a table entry restore path
> + * @its: its handle
> + * @id: id of the entry
> + * @entry: pointer to the entry
> + * @opaque: pointer to an opaque data
> + * @next_offset: minimal ID offset to the next entry. 0 if this
> + * entry is the last one, 1 if the entry is invalid, >= 1 if an
> + * entry's next_offset field was truly decoded
> + *
> + * Return: < 0 on error, 0 otherwise
> + */
> +typedef int (*entry_fn_t)(struct vgic_its *its, u32 id, void *entry,
> +			  void *opaque, u32 *next_offset);
> +
> +/**
> + * lookup_table - scan a contiguous table in guest RAM and applies a function
> + * to each entry
> + *
> + * @its: its handle
> + * @base: base gpa of the table
> + * @size: size of the table in bytes
> + * @esz: entry size in bytes
> + * @start_id: first entry's ID

I'm a little confused.  Why is this not 0?

> + * @fn: function to apply on each entry
> + *
> + * Return: < 0 on error, 1 if last element identified, 0 otherwise

How can you scan the entire table and not find the last element?

> + */
> +int lookup_table(struct vgic_its *its, gpa_t base, int size, int esz,
> +		 int start_id, entry_fn_t fn, void *opaque)

Is this really a lookup?  I think this should be called
'scan_its_table'.

> +{
> +	void *entry = kzalloc(esz, GFP_KERNEL);
> +	struct kvm *kvm = its->dev->kvm;
> +	unsigned long len = size;
> +	u32 id = start_id;

why are ids u32 and not just an unsigned long?

> +	gpa_t gpa = base;
> +	int ret;
> +
> +	while (len > 0) {
> +		u32 next_offset;
> +		size_t byte_offset;
> +
> +		ret = kvm_read_guest(kvm, gpa, entry, esz);
> +		if (ret)
> +			goto out;
> +
> +		ret = fn(its, id, entry, opaque, &next_offset);
> +		if (ret < 0 || (!ret && !next_offset))
> +			goto out;
> +
> +		byte_offset = next_offset * esz;
> +		id += next_offset;
> +		gpa += byte_offset;
> +		len -= byte_offset;
> +	}
> +	kfree(entry);
> +	return 0;
> +

here you can just set 'ret = 0;'

> +out:
> +	kfree(entry);
> +	return (ret < 0 ? ret : 1);

and then here you can do 'return (ret <= 0 ? ret : 1)'
but I actually think it's nicer to just write:

	if (ret <= 0)
		return ret;
	return 1;

> +}
> +
>  /**
>   * vgic_its_save_device_tables - Save the device table and all ITT
>   * into guest RAM
> -- 
> 2.5.5
> 

Thanks,
-Christoffer