Re: [PULL 1/3] vfio/pci: add support for VF token

["Cédric Le Goater" <clg@redhat.com>]

Hello Matthew,

On 5/23/23 18:51, Matthew Rosato wrote:
> On 5/9/23 5:59 PM, Alex Williamson wrote:
>> From: Minwoo Im <minwoo.im@samsung.com>
>>
>> VF token was introduced [1] to kernel vfio-pci along with SR-IOV
>> support [2].  This patch adds support VF token among PF and VF(s). To
>> passthu PCIe VF to a VM, kernel >= v5.7 needs this.
>>
>> It can be configured with UUID like:
>>
>>    -device vfio-pci,host=DDDD:BB:DD:F,vf-token=<uuid>,...
>>
>> [1] https://lore.kernel.org/linux-pci/158396393244.5601.10297430724964025753.stgit@gimli.home/
>> [2] https://lore.kernel.org/linux-pci/158396044753.5601.14804870681174789709.stgit@gimli.home/
>>
>> Cc: Alex Williamson <alex.williamson@redhat.com>
>> Signed-off-by: Minwoo Im <minwoo.im@samsung.com>
>> Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
>> Link: https://lore.kernel.org/r/20230320073522epcms2p48f682ecdb73e0ae1a4850ad0712fd780@epcms2p4
>> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> 
> Hi Minwoo, Alex,
> 
> I'm seeing a regression in vfio-pci on s390 and bisect points to this commit.  I don't believe it's specific to s390 though, but rather when not using this new vf-token, see below...
> 
>> ---
>>   hw/vfio/pci.c | 13 ++++++++++++-
>>   hw/vfio/pci.h |  1 +
>>   2 files changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>> index ec9a854361ac..cf27f28936cb 100644
>> --- a/hw/vfio/pci.c
>> +++ b/hw/vfio/pci.c
>> @@ -2856,6 +2856,8 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>>       int groupid;
>>       int i, ret;
>>       bool is_mdev;
>> +    char uuid[UUID_FMT_LEN];
>> +    char *name;
>>   
>>       if (!vbasedev->sysfsdev) {
>>           if (!(~vdev->host.domain || ~vdev->host.bus ||
>> @@ -2936,7 +2938,15 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>>           goto error;
>>       }
>>   
>> -    ret = vfio_get_device(group, vbasedev->name, vbasedev, errp);
>> +    if (!qemu_uuid_is_null(&vdev->vf_token)) {
>> +        qemu_uuid_unparse(&vdev->vf_token, uuid);
>> +        name = g_strdup_printf("%s vf_token=%s", vbasedev->name, uuid);
>> +    } else {
>> +        name = vbasedev->name;
> 
> ^ here we copy the pointer when a vf-token was not specified.
> 
>> +    }
>> +
>> +    ret = vfio_get_device(group, name, vbasedev, errp);
>> +    g_free(name);
> 
> ^ and then free it regardless.  But I don't think we meant to free what vbasedev->name points to, this was meant to free a duplicate string.  I'm subsequently seeing qemu crashes later on e.g. during device unplug.
> 
> I think doing a strdup in either case would fix the issue OR skipping the g_free when qemu_uuid_is_null(&vdev->vf_token).
> 
> FWIW, I tried the following and it resolved the issue for me:

Zhenzhong provided the exact same fix :

   https://lore.kernel.org/qemu-devel/20230517024651.82248-1-zhenzhong.duan@intel.com/

Thanks,

C.

> 
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index bf27a39905..73874a94de 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -2994,7 +2994,7 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>           qemu_uuid_unparse(&vdev->vf_token, uuid);
>           name = g_strdup_printf("%s vf_token=%s", vbasedev->name, uuid);
>       } else {
> -        name = vbasedev->name;
> +        name = g_strdup(vbasedev->name);
>       }
>   
>       ret = vfio_get_device(group, name, vbasedev, errp);
> 
> 
> 
>