Re: [PATCH v3 3/3] hisi_acc_vfio_pci: reject live migration on 64KB page with QM_HW_V3 hardware

[liulongfang <liulongfang@huawei.com>]

On 2026/8/31 18:00, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The patch completely breaks VFIO passthrough for this device on 64KB page hosts instead of gracefully falling back to generic operations.
> --
> 
> commit e0bfdb6998df9e209e0b7358693ec17f21c25bfe
> Author: Longfang Liu <liulongfang@huawei.com>
> 
> hisi_acc_vfio_pci: reject live migration on 64KB page with QM_HW_V3 hardware
> 
> This commit aims to prevent security vulnerabilities and guest exceptions when
> combining QM_HW_V3 hardware with 64KB pages by disabling live migration. It
> returns -EINVAL during device initialization if the host page size exceeds
> 32KB.
> 
>> diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> index 4abed2e49986f..4f12cab96545e 100644
>> --- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> +++ b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> @@ -1210,6 +1210,23 @@ static int hisi_acc_vf_qm_init(struct hisi_acc_vf_core_device *hisi_acc_vdev)
>>  	else
>>  		hisi_acc_vdev->drv_mode = HW_ACC_MIG_VF_CTRL;
>>  
>> +	/*
>> +	 * On VF_CTRL hardware, BAR2 holds 32KB functional + 32KB
>> +	 * migration registers. When the host page exceeds 32KB, the
>> +	 * two share one physical page and cannot be isolated by mmap.
>> +	 * Reject the open so QEMU fails cleanly at startup.
>> +	 */
>> +	if (hisi_acc_vdev->drv_mode == HW_ACC_MIG_VF_CTRL) {
>> +		resource_size_t func_len =
>> +			pci_resource_len(vf_dev, VFIO_PCI_BAR2_REGION_INDEX) >> 1;
>> +
>> +		if (func_len < PAGE_SIZE) {
>> +			dev_err(&vf_dev->dev,
>> +				"migration not supported on 64KB pages with QM_HW_V3\n");
>> +			return -EINVAL;
> 
> [Severity: High]
> Does returning an error here completely break VFIO passthrough for this device
> on 64KB page hosts?
> 
> Since hisi_acc_vf_qm_init() is called during device open, returning an error
> causes the entire operation to fail. This results in users completely losing
> passthrough functionality for QM_HW_V3 devices on 64KB page hosts, rather
> than just having migration gracefully disabled.
> 
> Could this be handled earlier in hisi_acc_vfio_pci_probe() instead?
> 
> The driver currently assigns migration operations unconditionally:
> 
> drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c:hisi_acc_vfio_pci_probe() {
>     ...
>     if (pf_qm && pf_qm->ver >= QM_HW_V3) {
>         if (pdev->is_virtfn)
>             ops = &hisi_acc_vfio_pci_migrn_ops;
>     ...
> }
> 
> If the 64KB page limitation was checked during probe and fell back to the
> generic ops instead, normal passthrough would continue to work correctly.
> The generic VFIO implementation safely maps the entire BAR2 region without
> KVM trap-and-emulate issues.
>

Our goal is precisely to disable live migration for passthrough on 64KB page systems.

Thanks
Longfang


>> +		}
>> +	}
>> +
>>  	if (hisi_acc_vdev->drv_mode == HW_ACC_MIG_PF_CTRL) {
>>  		/*
>>  		 * On hardware platforms greater than QM_HW_V3, the migration function
>