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

Auger Eric
2017-05-03T10:22:06Z

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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