Re: [dpdk-dev] [PATCH v3 18/19] vhost: add flag to enable postcopy live-migration

[Ilya Maximets <i.maximets@samsung.com>]

Have you missed this mail while preparing v4?

Best regards, Ilya Maximets.

On 05.10.2018 17:24, Ilya Maximets wrote:
> I think it'll be nice to have a warning in case zero-copy
> and postcopy enabled at the same time. This warning will
> clarify for users why postcopy is not enabled.
> What do you think?
> 
> Maybe we can also move the check from the previous patch to
> rte_vhost_driver_register() like it done for VIRTIO_F_IN_ORDER ?
> We can't change the set of enabled features in runtime anyway.
> 
> Best regards, Ilya Maximets.
> 
> On 04.10.2018 11:14, Maxime Coquelin wrote:
>> Postcopy live-migration feature require the application to
>> not populate the guest memory. As the vhost library cannot
>> prevent the application to that (e.g. preventing the
>> application to call mlockall()), the feature is disabled by
>> default.
>>
>> The application should only enable the feature if it does not
>> force the guest memory to be populated.
>>
>> In case the user passes the RTE_VHOST_USER_POSTCOPY_SUPPORT
>> flag at registration but the feature was not compiled,
>> registration fails.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>  doc/guides/prog_guide/vhost_lib.rst |  8 ++++++++
>>  lib/librte_vhost/rte_vhost.h        |  1 +
>>  lib/librte_vhost/socket.c           | 19 +++++++++++++++++--
>>  3 files changed, 26 insertions(+), 2 deletions(-)
>>
>> diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
>> index 77af4d775..c77df338f 100644
>> --- a/doc/guides/prog_guide/vhost_lib.rst
>> +++ b/doc/guides/prog_guide/vhost_lib.rst
>> @@ -106,6 +106,14 @@ The following is an overview of some key Vhost API functions:
>>      Enabling this flag with these Qemu version results in Qemu being blocked
>>      when multiple queue pairs are declared.
>>  
>> +  - ``RTE_VHOST_USER_POSTCOPY_SUPPORT``
>> +
>> +    Postcopy live-migration support will be enabled when this flag is set.
>> +    It is disabled by default.
>> +
>> +    Enabling this flag should only be done when the calling application does
>> +    not pre-fault the guest shared memory, otherwise migration would fail.
>> +
>>  * ``rte_vhost_driver_set_features(path, features)``
>>  
>>    This function sets the feature bits the vhost-user driver supports. The
>> diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
>> index b3cc6990d..b26afbffa 100644
>> --- a/lib/librte_vhost/rte_vhost.h
>> +++ b/lib/librte_vhost/rte_vhost.h
>> @@ -28,6 +28,7 @@ extern "C" {
>>  #define RTE_VHOST_USER_NO_RECONNECT	(1ULL << 1)
>>  #define RTE_VHOST_USER_DEQUEUE_ZERO_COPY	(1ULL << 2)
>>  #define RTE_VHOST_USER_IOMMU_SUPPORT	(1ULL << 3)
>> +#define RTE_VHOST_USER_POSTCOPY_SUPPORT		(1ULL << 4)
>>  
>>  /** Protocol features. */
>>  #ifndef VHOST_USER_PROTOCOL_F_MQ
>> diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
>> index c04d3d305..3df303be8 100644
>> --- a/lib/librte_vhost/socket.c
>> +++ b/lib/librte_vhost/socket.c
>> @@ -51,6 +51,8 @@ struct vhost_user_socket {
>>  	uint64_t supported_features;
>>  	uint64_t features;
>>  
>> +	uint64_t protocol_features;
>> +
>>  	/*
>>  	 * Device id to identify a specific backend device.
>>  	 * It's set to -1 for the default software implementation.
>> @@ -731,7 +733,7 @@ rte_vhost_driver_get_protocol_features(const char *path,
>>  	did = vsocket->vdpa_dev_id;
>>  	vdpa_dev = rte_vdpa_get_device(did);
>>  	if (!vdpa_dev || !vdpa_dev->ops->get_protocol_features) {
>> -		*protocol_features = VHOST_USER_PROTOCOL_FEATURES;
>> +		*protocol_features = vsocket->protocol_features;
>>  		goto unlock_exit;
>>  	}
>>  
>> @@ -744,7 +746,7 @@ rte_vhost_driver_get_protocol_features(const char *path,
>>  		goto unlock_exit;
>>  	}
>>  
>> -	*protocol_features = VHOST_USER_PROTOCOL_FEATURES
>> +	*protocol_features = vsocket->protocol_features
>>  		& vdpa_protocol_features;
>>  
>>  unlock_exit:
>> @@ -863,6 +865,7 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
>>  	vsocket->use_builtin_virtio_net = true;
>>  	vsocket->supported_features = VIRTIO_NET_SUPPORTED_FEATURES;
>>  	vsocket->features           = VIRTIO_NET_SUPPORTED_FEATURES;
>> +	vsocket->protocol_features  = VHOST_USER_PROTOCOL_FEATURES;
>>  
>>  	/* Dequeue zero copy can't assure descriptors returned in order */
>>  	if (vsocket->dequeue_zero_copy) {
>> @@ -875,6 +878,18 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
>>  		vsocket->features &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
>>  	}
>>  
>> +	if (!(flags & RTE_VHOST_USER_POSTCOPY_SUPPORT)) {
>> +		vsocket->protocol_features &=
>> +			~(1ULL << VHOST_USER_PROTOCOL_F_PAGEFAULT);
>> +	} else {
>> +#ifndef RTE_LIBRTE_VHOST_POSTCOPY
>> +		RTE_LOG(ERR, VHOST_CONFIG,
>> +			"Postcopy requested but not compiled\n");
>> +		ret = -1;
>> +		goto out_mutex;
>> +#endif
>> +	}
>> +
>>  	if ((flags & RTE_VHOST_USER_CLIENT) != 0) {
>>  		vsocket->reconnect = !(flags & RTE_VHOST_USER_NO_RECONNECT);
>>  		if (vsocket->reconnect && reconn_tid == 0) {
>>
> 
>