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

[Alex Williamson]

On Mon, 31 Aug 2026 17:09:51 +0800
Longfang Liu <liulongfang@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
>  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,

Alex