linux-kernel - Re: [PATCH] vp_vdpa: harden the logic of set status

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Date:   Fri, 11 Nov 2022 23:49:10 +0800
From:   "Longpeng (Mike, Cloud Infrastructure Service Product Dept.)" 
        <longpeng2@...wei.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
CC:     <stefanha@...hat.com>, <mst@...hat.com>, <jasowang@...hat.com>,
        <virtualization@...ts.linux-foundation.org>,
        <arei.gonglei@...wei.com>, <yechuan@...wei.com>,
        <huangzhichao@...wei.com>, <linux-kernel@...r.kernel.org>,
        <xiehong@...wei.com>
Subject: Re: [PATCH] vp_vdpa: harden the logic of set status



在 2022/11/11 23:14, Stefano Garzarella 写道:
> On Fri, Nov 11, 2022 at 10:55:05PM +0800, Longpeng(Mike) wrote:
>> From: Longpeng <longpeng2@...wei.com>
>>
>> 1. We should not set status to 0 when invoking vp_vdpa_set_status().
>>
>> 2. The driver MUST wait for a read of device_status to return 0 before
>>   reinitializing the device.
>>
>> Signed-off-by: Longpeng <longpeng2@...wei.com>
>> ---
>> drivers/vdpa/virtio_pci/vp_vdpa.c | 11 ++++++++++-
>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vdpa/virtio_pci/vp_vdpa.c 
>> b/drivers/vdpa/virtio_pci/vp_vdpa.c
>> index d448db0c4de3..d35fac5cde11 100644
>> --- a/drivers/vdpa/virtio_pci/vp_vdpa.c
>> +++ b/drivers/vdpa/virtio_pci/vp_vdpa.c
>> @@ -212,8 +212,12 @@ static void vp_vdpa_set_status(struct vdpa_device 
>> *vdpa, u8 status)
>> {
>>     struct vp_vdpa *vp_vdpa = vdpa_to_vp(vdpa);
>>     struct virtio_pci_modern_device *mdev = vp_vdpa_to_mdev(vp_vdpa);
>> -    u8 s = vp_vdpa_get_status(vdpa);
> 
> Is this change really needed?
> 
No need to get the status if we try to set status to 0 (trigger BUG).

>> +    u8 s;
>> +
>> +    /* We should never be setting status to 0. */
>> +    BUG_ON(status == 0);
> 
> IMHO panicking the kernel seems excessive in this case, please use 
> WARN_ON and maybe return earlier.
> 
Um...I referenced the vp_reset/vp_set_status,

>>
>> +    s = vp_vdpa_get_status(vdpa);
>>     if (status & VIRTIO_CONFIG_S_DRIVER_OK &&
>>         !(s & VIRTIO_CONFIG_S_DRIVER_OK)) {
>>         vp_vdpa_request_irq(vp_vdpa);
>> @@ -229,6 +233,11 @@ static int vp_vdpa_reset(struct vdpa_device *vdpa)
>>     u8 s = vp_vdpa_get_status(vdpa);
>>
>>     vp_modern_set_status(mdev, 0);
>> +    /* After writing 0 to device_status, the driver MUST wait for a 
>> read of
>> +     * device_status to return 0 before reinitializing the device.
>> +     */
>> +    while (vp_modern_get_status(mdev))
>> +        msleep(1);
> 
> Should we set a limit after which we give up? A malfunctioning device 
> could keep us here forever.
> 
Yes, but the malfunctioning device maybe can not work anymore, how to 
handle it?

> Thanks,
> Stefano
> 
>>
>>     if (s & VIRTIO_CONFIG_S_DRIVER_OK)
>>         vp_vdpa_free_irq(vp_vdpa);
>> -- 
>> 2.23.0
>>
> 
> .