Re: [PATCH v5 1/2] hisi_acc_vfio_pci: fix NULL dereference in reset_prepare on PF passthrough

[liulongfang]

On 2026/9/30 5:51, Alex Williamson wrote:
> On Wed, 23 Sep 2026 16:25:50 +0800
> Longfang Liu <liulongfang@xxxxxxxxxx> wrote:
> 
>> When a PF is bound to the driver via driver_override and passed
>> through to a VM, its pf_qm stays NULL. The PCI error handler
>> reset_prepare() runs during open_device through
>> pci_try_reset_function(), before the mig_ops gate, and dereferences
>> the NULL pf_qm for the timeout log, crashing the kernel.
>>
>> Move the mig_ops check to the entry of reset_prepare() and
>> aer_reset_done() so non-migration devices skip the QM_RESETTING
>> coordination. Also clear set_reset_flag together with QM_RESETTING
>> in aer_reset_done(); the flag was never cleared before, so a later
>> timed-out reset could release a foreign lock.
>>
>> Fixes: b0eed085903e ("hisi_acc_vfio_pci: Add support for VFIO live migration")
>> Fixes: a22099ed7936f ("hisi_acc_vfio_pci: fix VF reset timeout issue")
>> Signed-off-by: Longfang Liu <liulongfang@xxxxxxxxxx>
>> ---
>>  drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c | 11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> index 86362ec424a5..6a09252258b9 100644
>> --- a/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> +++ b/drivers/vfio/pci/hisilicon/hisi_acc_vfio_pci.c
>> @@ -1157,6 +1157,9 @@ static void hisi_acc_vf_pci_reset_prepare(struct pci_dev *pdev)
> 
> Rolling back to one more line of context in this function:
> 
> 	struct hisi_qm *qm = hisi_acc_vdev->pf_qm;
> 
> As per the commit log, we're trying to fix a problem where pf_qm is
> NULL and dereferenced, such as in this next line:
> 
>>  	struct device *dev = &qm->pdev->dev;
>>  	u32 delay = 0;
>>  
>> +	if (!hisi_acc_vdev->core_device.vdev.mig_ops)
>> +		return;
>> +
>>  	/* All reset requests need to be queued for processing */
>>  	while (test_and_set_bit(QM_RESETTING, &qm->misc_ctl)) {
>>  		msleep(1);
> 
> Further context:
> 
>                 if (++delay > QM_RESET_WAIT_TIMEOUT) {
>                         dev_err(dev, "reset prepare failed\n");
>                         return;
>                 }
> 
> So the added test exits before the inline dereference testing
> QM_RESETTING, but you're relying on the compiler to move the resolution
> of dev into the branch here.  The dereference bug is not fully
> resolved, it's only masked by the compiler optimization.
> 
> The easy solution is to either move the struct device deref into the
> branch where it's needed, or (better) just open code &qm->pdev->dev on
> the dev_err() call.  Thanks,
>

OK, your analysis is correct.
I will directly update the dev_err() call to use &qm->pdev->dev in the next version.

Thanks!
Longfang.

> Alex
> 
>> @@ -1174,12 +1177,14 @@ static void hisi_acc_vf_pci_aer_reset_done(struct pci_dev *pdev)
>>  	struct hisi_acc_vf_core_device *hisi_acc_vdev = hisi_acc_drvdata(pdev);
>>  	struct hisi_qm *qm = hisi_acc_vdev->pf_qm;
>>  
>> -	if (hisi_acc_vdev->set_reset_flag)
>> -		clear_bit(QM_RESETTING, &qm->misc_ctl);
>> -
>>  	if (!hisi_acc_vdev->core_device.vdev.mig_ops)
>>  		return;
>>  
>> +	if (hisi_acc_vdev->set_reset_flag) {
>> +		clear_bit(QM_RESETTING, &qm->misc_ctl);
>> +		hisi_acc_vdev->set_reset_flag = false;
>> +	}
>> +
>>  	mutex_lock(&hisi_acc_vdev->state_mutex);
>>  	hisi_acc_vf_reset(hisi_acc_vdev);
>>  	mutex_unlock(&hisi_acc_vdev->state_mutex);
> 
> .
>