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

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On Tuesday, February 20, 2024 9:25 PM, Jason Gunthorpe wrote:
> To: Zeng, Xin <xin.zeng@xxxxxxxxx>
> Cc: Yishai Hadas <yishaih@xxxxxxxxxx>; herbert@xxxxxxxxxxxxxxxxxxx;
> alex.williamson@xxxxxxxxxx; shameerali.kolothum.thodi@xxxxxxxxxx; Tian,
> Kevin <kevin.tian@xxxxxxxxx>; linux-crypto@xxxxxxxxxxxxxxx;
> kvm@xxxxxxxxxxxxxxx; qat-linux <qat-linux@xxxxxxxxx>; Cao, Yahui
> <yahui.cao@xxxxxxxxx>
> 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






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