Re: [PATCH 10/10] vfio/qat: Add vfio_pci driver for Intel QAT VF devices

Jason Gunthorpe
2024-02-20T17:03:21Z

On Tue, Feb 20, 2024 at 03:53:08PM +0000, Zeng, Xin wrote:
> On Tuesday, February 20, 2024 9:25 PM, Jason Gunthorpe wrote:
> > To: Zeng, Xin <xin.zeng@intel.com>
> > Cc: Yishai Hadas <yishaih@nvidia.com>; herbert@gondor.apana.org.au;
> > alex.williamson@redhat.com; shameerali.kolothum.thodi@huawei.com; Tian,
> > Kevin <kevin.tian@intel.com>; linux-crypto@vger.kernel.org;
> > kvm@vger.kernel.org; qat-linux <qat-linux@intel.com>; Cao, Yahui
> > <yahui.cao@intel.com>
> > Subject: Re: [PATCH 10/10] vfio/qat: Add vfio_pci driver for Intel QAT VF devices
> >
> > On Sat, Feb 17, 2024 at 04:20:20PM +0000, Zeng, Xin wrote:
> >
> > > Thanks for this information, but this flow is not clear to me why it
> > > cause deadlock. From this flow, CPU0 is not waiting for any resource
> > > held by CPU1, so after CPU0 releases mmap_lock, CPU1 can continue
> > > to run. Am I missing something?
> >
> > At some point it was calling copy_to_user() under the state
> > mutex. These days it doesn't.
> >
> > copy_to_user() would nest the mm_lock under the state mutex which is a
> > locking inversion.
> >
> > So I wonder if we still have this problem now that the copy_to_user()
> > is not under the mutex?
>
> In protocol v2, we still have the scenario in precopy_ioctl where copy_to_user is
> called under state_mutex.

Why? Does mlx5 do that? It looked Ok to me:

mlx5vf_state_mutex_unlock(mvdev);
if (copy_to_user((void __user *)arg, &info, minsz))
return -EFAULT;

Jason