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

[sashiko-bot@kernel.org]

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.
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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.

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

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260831090951.844569-1-liulongfang@huawei.com?part=3