Messages in this thread | | | Subject | Re: [PATCH RFC 4/5] vhost-vdpa: support IOTLB batching hints | From | Jason Wang <> | Date | Tue, 30 Jun 2020 09:55:23 +0800 |
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On 2020/6/29 下午11:49, Michael S. Tsirkin wrote: > On Mon, Jun 29, 2020 at 05:26:03PM +0800, Jason Wang wrote: >> On 2020/6/28 下午5:58, Michael S. Tsirkin wrote: >>> On Thu, Jun 18, 2020 at 01:56:25PM +0800, Jason Wang wrote: >>>> This patches extend the vhost IOTLB API to accept batch updating hints >>>> form userspace. When userspace wants update the device IOTLB in a >>>> batch, it may do: >>>> >>>> 1) Write vhost_iotlb_msg with VHOST_IOTLB_BATCH_BEGIN flag >>>> 2) Perform a batch of IOTLB updating via VHOST_IOTLB_UPDATE/INVALIDATE >>>> 3) Write vhost_iotlb_msg with VHOST_IOTLB_BATCH_END flag >>> As long as we are extending the interface, >>> is there some way we could cut down the number of system calls needed >>> here? >> >> I'm not sure it's worth to do that since usually we only have less than 10 >> regions. > > Well with a guest iommu I'm guessing it can go up significantly, right?
The batching flag is not mandatory, so userspace can still choose to update a single IOTLB mapping through a single system call without batch flag.
> >> A possible method is to carry multiple vhost_iotlb_message in one system >> call. > That's an option. > Also, can kernel handle a batch that is too large by applying > parts of it iteratively?
I think so, we can iterate a vhost iotlb message one by one through iov iterator.
> Or must all changes take place atomically after BATCH_END?
For changes:
- if you mean the changes in vhost IOTLB, it's not atomically - if you mean the mapping seen by vDPA device driver, it could be atomically for the device driver that implements set_map() method, since we pass a interval tree to the device.
> If atomically, we might need to limit batch size to make > sure kernel can keep a copy in memory.
It's the responsibility of guest driver to make sure there won't be a race condition between DMA and map updating. So it looks to me we don't need to care about that.
> > >>> >>>> Vhost-vdpa may decide to batch the IOMMU/IOTLB updating in step 3 when >>>> vDPA device support set_map() ops. This is useful for the vDPA device >>>> that want to know all the mappings to tweak their own DMA translation >>>> logic. >>>> >>>> For vDPA device that doesn't require set_map(), no behavior changes. >>>> >>>> This capability is advertised via VHOST_BACKEND_F_IOTLB_BATCH capability. >>>> >>>> Signed-off-by: Jason Wang <jasowang@redhat.com> >>>> --- >>>> drivers/vhost/vdpa.c | 30 +++++++++++++++++++++++------- >>>> include/uapi/linux/vhost.h | 2 ++ >>>> include/uapi/linux/vhost_types.h | 7 +++++++ >>>> 3 files changed, 32 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c >>>> index 453057421f80..8f624bbafee7 100644 >>>> --- a/drivers/vhost/vdpa.c >>>> +++ b/drivers/vhost/vdpa.c >>>> @@ -56,7 +56,9 @@ enum { >>>> }; >>>> enum { >>>> - VHOST_VDPA_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2) >>>> + VHOST_VDPA_BACKEND_FEATURES = >>>> + (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2) | >>>> + (1ULL << VHOST_BACKEND_F_IOTLB_BATCH), >>>> }; >>>> /* Currently, only network backend w/o multiqueue is supported. */ >>>> @@ -77,6 +79,7 @@ struct vhost_vdpa { >>>> int virtio_id; >>>> int minor; >>>> struct eventfd_ctx *config_ctx; >>>> + int in_batch; >>>> }; >>>> static DEFINE_IDA(vhost_vdpa_ida); >>>> @@ -125,6 +128,7 @@ static void vhost_vdpa_reset(struct vhost_vdpa *v) >>>> const struct vdpa_config_ops *ops = vdpa->config; >>>> ops->set_status(vdpa, 0); >>>> + v->in_batch = 0; >>>> } >>>> static long vhost_vdpa_get_device_id(struct vhost_vdpa *v, u8 __user *argp) >>>> @@ -540,9 +544,10 @@ static int vhost_vdpa_map(struct vhost_vdpa *v, >>>> if (ops->dma_map) >>>> r = ops->dma_map(vdpa, iova, size, pa, perm); >>>> - else if (ops->set_map) >>>> - r = ops->set_map(vdpa, dev->iotlb); >>>> - else >>>> + else if (ops->set_map) { >>>> + if (!v->in_batch) >>>> + r = ops->set_map(vdpa, dev->iotlb); >>>> + } else >>>> r = iommu_map(v->domain, iova, pa, size, >>>> perm_to_iommu_flags(perm)); >>>> @@ -559,9 +564,10 @@ static void vhost_vdpa_unmap(struct vhost_vdpa *v, u64 iova, u64 size) >>>> if (ops->dma_map) >>>> ops->dma_unmap(vdpa, iova, size); >>>> - else if (ops->set_map) >>>> - ops->set_map(vdpa, dev->iotlb); >>>> - else >>>> + else if (ops->set_map) { >>>> + if (!v->in_batch) >>>> + ops->set_map(vdpa, dev->iotlb); >>>> + } else >>>> iommu_unmap(v->domain, iova, size); >>>> } >>>> @@ -655,6 +661,8 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev, >>>> struct vhost_iotlb_msg *msg) >>>> { >>>> struct vhost_vdpa *v = container_of(dev, struct vhost_vdpa, vdev); >>>> + struct vdpa_device *vdpa = v->vdpa; >>>> + const struct vdpa_config_ops *ops = vdpa->config; >>>> int r = 0; >>>> r = vhost_dev_check_owner(dev); >>>> @@ -668,6 +676,14 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev *dev, >>>> case VHOST_IOTLB_INVALIDATE: >>>> vhost_vdpa_unmap(v, msg->iova, msg->size); >>>> break; >>>> + case VHOST_IOTLB_BATCH_BEGIN: >>>> + v->in_batch = true; >>>> + break; >>>> + case VHOST_IOTLB_BATCH_END: >>>> + if (v->in_batch && ops->set_map) >>>> + ops->set_map(vdpa, dev->iotlb); >>>> + v->in_batch = false; >>>> + break; >>>> default: >>>> r = -EINVAL; >>>> break; >>>> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h >>>> index 0c2349612e77..565da96f55d5 100644 >>>> --- a/include/uapi/linux/vhost.h >>>> +++ b/include/uapi/linux/vhost.h >>>> @@ -91,6 +91,8 @@ >>>> /* Use message type V2 */ >>>> #define VHOST_BACKEND_F_IOTLB_MSG_V2 0x1 >>>> +/* IOTLB can accpet batching hints */ >>> typo >> >> Will fix. >> >> >>>> +#define VHOST_BACKEND_F_IOTLB_BATCH 0x2 >>>> #define VHOST_SET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x25, __u64) >>>> #define VHOST_GET_BACKEND_FEATURES _IOR(VHOST_VIRTIO, 0x26, __u64) >>>> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h >>>> index 669457ce5c48..5c12faffdde9 100644 >>>> --- a/include/uapi/linux/vhost_types.h >>>> +++ b/include/uapi/linux/vhost_types.h >>>> @@ -60,6 +60,13 @@ struct vhost_iotlb_msg { >>>> #define VHOST_IOTLB_UPDATE 2 >>>> #define VHOST_IOTLB_INVALIDATE 3 >>>> #define VHOST_IOTLB_ACCESS_FAIL 4 >>>> +/* VHOST_IOTLB_BATCH_BEGIN is a hint that userspace will update >>>> + * several mappings afterwards. VHOST_IOTLB_BATCH_END is a hint that >>>> + * userspace had finished the mapping updating. >>> Well not just hints - in fact updates do not take place >>> until _END. >>> >>> How about: >>> >>> /* VHOST_IOTLB_BATCH_BEGIN and VHOST_IOTLB_BATCH_END allow modifying >>> * multiple mappings in one go: beginning with >>> * VHOST_IOTLB_BATCH_BEGIN, followed by any number of >>> VHOST_IOTLB_UPDATE messages, and ending with VHOST_IOTLB_BATCH_END. >>> */ >> >> That's better. > > Is there a guarantee that these changes take place atomically? > Let's document that.
There's no guarantee. Will document this.
Thanks
> >>> >>>> When those two flags >>>> + * were set, kernel will ignore the rest fileds of the IOTLB message. >>> how about: >>> >>> when one of these two values is used as the message type, the >>> rest of the fields in the message are ignored. >> >> Yes. >> >> Will fix. >> >> Thanks >> >> >>>> + */ >>>> +#define VHOST_IOTLB_BATCH_BEGIN 5 >>>> +#define VHOST_IOTLB_BATCH_END 6 >>>> __u8 type; >>>> }; >>>> -- >>>> 2.20.1
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