linux-kernel - Re: [PATCH v6 5/5] hisi_acc_vfio_pci: bugfix live migration function without VF device driver

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Message-ID: <96c36c66-37a6-7bdb-75b8-dd7d6f63bb35@huawei.com>
Date: Fri, 28 Mar 2025 16:28:33 +0800
From: liulongfang <liulongfang@...wei.com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: <jgg@...dia.com>, <shameerali.kolothum.thodi@...wei.com>,
	<jonathan.cameron@...wei.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linuxarm@...neuler.org>
Subject: Re: [PATCH v6 5/5] hisi_acc_vfio_pci: bugfix live migration function
 without VF device driver

On 2025/3/21 23:52, Alex Williamson wrote:
> On Tue, 18 Mar 2025 14:45:48 +0800
> Longfang Liu <liulongfang@...wei.com> wrote:
> 
>> If the VF device driver is not loaded in the Guest OS and we attempt to
>> perform device data migration, the address of the migrated data will
>> be NULL.
>> The live migration recovery operation on the destination side will
>> access a null address value, which will cause access errors.
>>
>> Therefore, live migration of VMs without added VF device drivers
>> does not require device data migration.
>> In addition, when the queue address data obtained by the destination
>> is empty, device queue recovery processing will not be performed.
>>
>> Fixes: b0eed085903e ("hisi_acc_vfio_pci: Add support for VFIO live migration")
>> Signed-off-by: Longfang Liu <liulongfang@...wei.com>
>> Reviewed-by: Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>
>> ---
>>  .../vfio/pci/hisilicon/hisi_acc_vfio_pci.c    | 21 ++++++++++++-------
>>  1 file changed, 14 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> index cadc82419dca..68b1c7204cad 100644
>> --- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> +++ b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> @@ -426,13 +426,6 @@ static int vf_qm_check_match(struct hisi_acc_vf_core_device *hisi_acc_vdev,
>>  		return -EINVAL;
>>  	}
>>  
>> -	ret = qm_write_regs(vf_qm, QM_VF_STATE, &vf_data->vf_qm_state, 1);
>> -	if (ret) {
>> -		dev_err(dev, "failed to write QM_VF_STATE\n");
>> -		return ret;
>> -	}
>> -
>> -	hisi_acc_vdev->vf_qm_state = vf_data->vf_qm_state;
>>  	hisi_acc_vdev->match_done = true;
>>  	return 0;
>>  }
>> @@ -498,6 +491,13 @@ static int vf_qm_load_data(struct hisi_acc_vf_core_device *hisi_acc_vdev,
>>  	if (migf->total_length < sizeof(struct acc_vf_data))
>>  		return -EINVAL;
>>  
>> +	ret = qm_write_regs(qm, QM_VF_STATE, &vf_data->vf_qm_state, 1);
>> +	if (ret) {
>> +		dev_err(dev, "failed to write QM_VF_STATE\n");
>> +		return -EINVAL;
>> +	}
>> +	hisi_acc_vdev->vf_qm_state = vf_data->vf_qm_state;
>> +
>>  	qm->eqe_dma = vf_data->eqe_dma;
>>  	qm->aeqe_dma = vf_data->aeqe_dma;
>>  	qm->sqc_dma = vf_data->sqc_dma;
>> @@ -506,6 +506,12 @@ static int vf_qm_load_data(struct hisi_acc_vf_core_device *hisi_acc_vdev,
>>  	qm->qp_base = vf_data->qp_base;
>>  	qm->qp_num = vf_data->qp_num;
>>  
>> +	if (!vf_data->eqe_dma || !vf_data->aeqe_dma ||
>> +	    !vf_data->sqc_dma || !vf_data->cqc_dma) {
>> +		dev_err(dev, "resume dma addr is NULL!\n");
>> +		return -EINVAL;
>> +	}
>> +
> 
> I'm not sure how this fits in based on the commit log.  IIUC, we're
> actually rejecting the migration data here, which will cause a
> migration failure.  We're also testing the validity of the data *after*
> we've actually applied it to the hisi_qm object, which seems backwards.
> 
> Are we just not processing the migration data because there's no driver
> or are we failing the migration?  There shouldn't be a requirement on
> the state of the guest driver for a successful migration.  Thanks,
>

Therefore, this shouldn't be about exiting the migration operation,
but rather continuing the migration process while skipping these empty
address write operations.
Consequently, this shouldn't return an error,
it should simply return 0.

Thanks.
Longfang.

> Alex
> 
>>  	ret = qm_set_regs(qm, vf_data);
>>  	if (ret) {
>>  		dev_err(dev, "set VF regs failed\n");
>> @@ -1531,6 +1537,7 @@ static int hisi_acc_vfio_pci_migrn_init_dev(struct vfio_device *core_vdev)
>>  	hisi_acc_vdev->vf_id = pci_iov_vf_id(pdev) + 1;
>>  	hisi_acc_vdev->pf_qm = pf_qm;
>>  	hisi_acc_vdev->vf_dev = pdev;
>> +	hisi_acc_vdev->vf_qm_state = QM_NOT_READY;
>>  	mutex_init(&hisi_acc_vdev->state_mutex);
>>  	mutex_init(&hisi_acc_vdev->open_mutex);
>>  
> 
> 
> 
> .
>