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

Auger Eric
2017-05-03T13:40:34Z

Hi Christoffer,

On 30/04/2017 21:33, 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
>> + * 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);
>
> Just noticed. All the table entries are 64-bit long at this point,
> right? So why not make entry a u64 * instead? Could we end up with
> some endianness mess with using void pointers the way it is now?
the size of the entry is ABI dependent while this infrastructure is
generic. In each of such function we use

u64 entry = *(u64 *)addr;
and we do a le64_to_cpu(entry).

Do you see something wrong? Otherwise I would be tempted to leave as is.

Thanks

Eric
>
> Thanks,
> -Christoffer
>
>> +
>> +/**
>> + * 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
>> + * @fn: function to apply on each entry
>> + *
>> + * Return: < 0 on error, 1 if last element identified, 0 otherwise
>> + */
>> +int lookup_table(struct vgic_its *its, gpa_t base, int size, int esz,
>> + int start_id, entry_fn_t fn, void *opaque)
>> +{
>> + void *entry = kzalloc(esz, GFP_KERNEL);
>> + struct kvm *kvm = its->dev->kvm;
>> + unsigned long len = size;
>> + u32 id = start_id;
>> + 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;
>> +
>> +out:
>> + kfree(entry);
>> + return (ret < 0 ? ret : 1);
>> +}
>> +
>> /**
>> * vgic_its_save_device_tables - Save the device table and all ITT
>> * into guest RAM
>> --
>> 2.5.5
>>