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 2026/9/12 1:37, Alex Williamson wrote:
> On Mon, 31 Aug 2026 17:09:51 +0800
> Longfang Liu <liulongfang@huawei.com> wrote:
> 
>> In the scenario combining QM_HW_V3 hardware with 64KB large pages, the
>> device functional region and migration registers share the BAR2 physical
>> page, resulting in a lack of isolation that triggers security issues.
>> More critically, since KVM does not support the specific 16-byte read/write
>> instructions used by the guest driver, operating under the KVM emulated
>> device scheme will lead to Guest kernel calltrace issues.
>> To prevent Guest exceptions and avoid security vulnerabilities, the
>> driver directly disables live migration functionality in this scenario.
>> This ensures the system fails cleanly with an error early during startup,
>> while other configuration modes remain unaffected and can still utilize
>> passthrough functionality normally.
>>
>> Fixes: b0eed085903e ("hisi_acc_vfio_pci: Add support for VFIO live migration")
>> Signed-off-by: Longfang Liu <liulongfang@huawei.com>
>> ---
>>  drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c | 17 +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>>
>> diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> index 4abed2e49986..4f12cab96545 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;
>> +		}
>> +	}
>> +
> 
> Sashiko correctly identifies that this breaks any assignment on 64K
> pages, which is contradictory to the comment that indicates this is
> only intended to disable migration support.  This should instead be
> invoking the non-migration path in the probe function.  Thanks,
>

It is a reasonable approach to directly select the non-migration ops in the probe
function based on the logic check.
I plan to implement this in the next revision and complete testing and verification.

Thanks.
Longfang.

> Alex
> 
> .
>