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

[Auger Eric <eric.auger@redhat.com>]

Hi Christoffer,

On 03/05/2017 10:01, Christoffer Dall wrote:
> On Wed, May 03, 2017 at 08:53:36AM +0200, Auger Eric wrote:
>> Hi Christoffer,
>>
>> On 30/04/2017 21:35, Christoffer Dall wrote:
>>> 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@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
>>>
>>> eh, also, did you mean -1 if the entry is invalid?
>> no in case the entry is invalid, we tell the caller that it must inspect
>> the next entry, hence the next_offset = +1.
> jjjjj
> hmm, but you say aftterwards that >= 1 if an entry's next_offset field
> was truly decoded, so this is confusing.  Perhaps it would make more
> sense to get rid of the parameter entirely and change the return value
> to say:
> 
>   Return: < 0 on error, 0 if the entry was the last one, and > 0 to
>           indicate the offset to the next entry that must be processed
> 	  when scanning a table.
> 
>   Note that we return 1 for an invalid entry, because scanning a table
>   in this case simply requires us looking at the next entry, but we may
>   return >= to 1 if we found a valid entry and decoded the next field in
>   the entry.
> 
> What do you think?
Yes I'm going to experiment that change.

Thanks

Eric
> 
> Thanks,
> -Christoffer
> 
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