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

Zeng, Xin
2024-02-20T15:53:13Z

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.

Thanks,
Xin