From: Si-Wei Liu <si-wei.liu@oracle.com>
To: Eugenio Perez Martin <eperezma@redhat.com>
Cc: qemu-devel@nongnu.org, "Michael S. Tsirkin" <mst@redhat.com>,
Lei Yang <leiyang@redhat.com>, Peter Xu <peterx@redhat.com>,
Jonah Palmer <jonah.palmer@oracle.com>,
Dragos Tatulea <dtatulea@nvidia.com>,
Jason Wang <jasowang@redhat.com>
Subject: Re: [RFC 1/2] iova_tree: add an id member to DMAMap
Date: Fri, 19 Apr 2024 16:49:45 -0700 [thread overview]
Message-ID: <450d0da1-3d11-428b-bd89-d09a2964cdb1@oracle.com> (raw)
In-Reply-To: <CAJaqyWeE3kfgN5Y0=Kj6oCOFwg0H-gQEr4g3TM+3_+5N7mfd=A@mail.gmail.com>
On 4/19/2024 1:29 AM, Eugenio Perez Martin wrote:
> On Thu, Apr 18, 2024 at 10:46 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>>
>>
>> On 4/10/2024 3:03 AM, Eugenio Pérez wrote:
>>> IOVA tree is also used to track the mappings of virtio-net shadow
>>> virtqueue. This mappings may not match with the GPA->HVA ones.
>>>
>>> This causes a problem when overlapped regions (different GPA but same
>>> translated HVA) exists in the tree, as looking them by HVA will return
>>> them twice. To solve this, create an id member so we can assign unique
>>> identifiers (GPA) to the maps.
>>>
>>> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
>>> ---
>>> include/qemu/iova-tree.h | 5 +++--
>>> util/iova-tree.c | 3 ++-
>>> 2 files changed, 5 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/include/qemu/iova-tree.h b/include/qemu/iova-tree.h
>>> index 2a10a7052e..34ee230e7d 100644
>>> --- a/include/qemu/iova-tree.h
>>> +++ b/include/qemu/iova-tree.h
>>> @@ -36,6 +36,7 @@ typedef struct DMAMap {
>>> hwaddr iova;
>>> hwaddr translated_addr;
>>> hwaddr size; /* Inclusive */
>>> + uint64_t id;
>>> IOMMUAccessFlags perm;
>>> } QEMU_PACKED DMAMap;
>>> typedef gboolean (*iova_tree_iterator)(DMAMap *map);
>>> @@ -100,8 +101,8 @@ const DMAMap *iova_tree_find(const IOVATree *tree, const DMAMap *map);
>>> * @map: the mapping to search
>>> *
>>> * Search for a mapping in the iova tree that translated_addr overlaps with the
>>> - * mapping range specified. Only the first found mapping will be
>>> - * returned.
>>> + * mapping range specified and map->id is equal. Only the first found
>>> + * mapping will be returned.
>>> *
>>> * Return: DMAMap pointer if found, or NULL if not found. Note that
>>> * the returned DMAMap pointer is maintained internally. User should
>>> diff --git a/util/iova-tree.c b/util/iova-tree.c
>>> index 536789797e..0863e0a3b8 100644
>>> --- a/util/iova-tree.c
>>> +++ b/util/iova-tree.c
>>> @@ -97,7 +97,8 @@ static gboolean iova_tree_find_address_iterator(gpointer key, gpointer value,
>>>
>>> needle = args->needle;
>>> if (map->translated_addr + map->size < needle->translated_addr ||
>>> - needle->translated_addr + needle->size < map->translated_addr) {
>>> + needle->translated_addr + needle->size < map->translated_addr ||
>>> + needle->id != map->id) {
>> It looks this iterator can also be invoked by SVQ from
>> vhost_svq_translate_addr() -> iova_tree_find_iova(), where guest GPA
>> space will be searched on without passing in the ID (GPA), and exact
>> match for the same GPA range is not actually needed unlike the mapping
>> removal case. Could we create an API variant, for the SVQ lookup case
>> specifically? Or alternatively, add a special flag, say skip_id_match to
>> DMAMap, and the id match check may look like below:
>>
>> (!needle->skip_id_match && needle->id != map->id)
>>
>> I think vhost_svq_translate_addr() could just call the API variant or
>> pass DMAmap with skip_id_match set to true to svq_iova_tree_find_iova().
>>
> I think you're totally right. But I'd really like to not complicate
> the API of the iova_tree more.
>
> I think we can look for the hwaddr using memory_region_from_host and
> then get the hwaddr. It is another lookup though...
Yeah, that will be another means of doing translation without having to
complicate the API around iova_tree. I wonder how the lookup through
memory_region_from_host() may perform compared to the iova tree one, the
former looks to be an O(N) linear search on a linked list while the
latter would be roughly O(log N) on an AVL tree? Of course,
memory_region_from_host() won't search out of the guest memory space for
sure. As this could be on the hot data path I have a little bit
hesitance over the potential cost or performance regression this change
could bring in, but maybe I'm overthinking it too much...
Thanks,
-Siwei
>
>> Thanks,
>> -Siwei
>>> return false;
>>> }
>>>
next prev parent reply other threads:[~2024-04-19 23:50 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-10 10:03 [RFC 0/2] Identify aliased maps in vdpa SVQ iova_tree Eugenio Pérez
2024-04-10 10:03 ` [RFC 1/2] iova_tree: add an id member to DMAMap Eugenio Pérez
2024-04-18 20:46 ` Si-Wei Liu
2024-04-19 8:29 ` Eugenio Perez Martin
2024-04-19 23:49 ` Si-Wei Liu [this message]
2024-04-22 8:49 ` Eugenio Perez Martin
2024-04-23 22:20 ` Si-Wei Liu
2024-04-24 7:33 ` Eugenio Perez Martin
2024-04-25 17:43 ` Si-Wei Liu
2024-04-29 8:14 ` Eugenio Perez Martin
2024-04-29 11:19 ` Jonah Palmer
2024-04-30 18:11 ` Eugenio Perez Martin
2024-05-01 22:08 ` Si-Wei Liu
2024-05-02 6:18 ` Eugenio Perez Martin
2024-05-07 9:12 ` Si-Wei Liu
2024-04-30 5:54 ` Si-Wei Liu
2024-04-30 17:19 ` Eugenio Perez Martin
2024-05-01 23:13 ` Si-Wei Liu
2024-05-02 6:44 ` Eugenio Perez Martin
2024-05-08 0:52 ` Si-Wei Liu
2024-05-08 15:25 ` Eugenio Perez Martin
2024-04-10 10:03 ` [RFC 2/2] vdpa: identify aliased maps in iova_tree Eugenio Pérez
2024-04-12 6:46 ` [RFC 0/2] Identify aliased maps in vdpa SVQ iova_tree Jason Wang
2024-04-12 7:56 ` Eugenio Perez Martin
2024-05-07 7:29 ` Jason Wang
2024-05-07 10:56 ` Eugenio Perez Martin
2024-05-08 2:29 ` Jason Wang
2024-05-08 17:15 ` Eugenio Perez Martin
2024-05-09 6:27 ` Jason Wang
2024-05-09 7:10 ` Eugenio Perez Martin
2024-05-10 4:28 ` Jason Wang
2024-05-10 7:16 ` Eugenio Perez Martin
2024-05-11 4:00 ` Jason Wang
2024-05-13 6:27 ` Eugenio Perez Martin
2024-05-13 8:28 ` Jason Wang
2024-05-13 9:56 ` Eugenio Perez Martin
2024-05-14 3:56 ` Jason Wang
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