linux-kernel - Re: [PATCH v3 0/1] vfio: remove VFIO_GROUP_NOTIFY_SET

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Date:   Tue, 24 May 2022 10:07:45 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>
Cc:     jgg@...dia.com, cohuck@...hat.com, borntraeger@...ux.ibm.com,
        jjherne@...ux.ibm.com, akrowiak@...ux.ibm.com, pasic@...ux.ibm.com,
        zhenyuw@...ux.intel.com, zhi.a.wang@...el.com, hch@...radead.org,
        intel-gfx@...ts.freedesktop.org,
        intel-gvt-dev@...ts.freedesktop.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/1] vfio: remove VFIO_GROUP_NOTIFY_SET_KVM

On Thu, 19 May 2022 14:33:10 -0400
Matthew Rosato <mjrosato@...ux.ibm.com> wrote:

> As discussed in this thread:
> 
> https://lore.kernel.org/kvm/20220516172734.GE1343366@nvidia.com/
> 
> Let's remove VFIO_GROUP_NOTIFY_SET_KVM and instead assume the association
> has already been established prior to device_open.  For the types today
> that need a KVM (GVT, vfio-ap) these will fail if a KVM is not found.
> Looking ahead, vfio-pci-zdev will optionally want the KVM association
> (enable hardware assists) but it will not be a hard requirement (still
> want to allow other, non-KVM userspace usage). 
> 
> This is built on top of vfio-next and tested with s390x-pci
> (zdev-kvm series) and vfio-ap (GVT changes are compile-tested only)
> 
> Changes for v3:
> - merge branches under if (device->open_count == 1) (Kevin)
> - move device->open_count-- out from group_rwsem (Kevin)
> - drop null KVM check (Christoph)
> - remove extra kvm_{get,put}_kvm from vfio_ap_ops, it was already getting
>   a reference (Jason)
> - Add comment about kvm reference in vfio.h (Jason)
> - Return -EINVAL if !kvm for vfio-ap (Tony)
> 
> Changes for v2:
> - gvt no longer needs release_work, get rid of it (Christoph)
> - a few compile fixes for gvt
> - update commit to mention fixes gvt oops (Jason)
> - s/down_write/down_read/ in a few spots (Jason)
> - avoid kvm build dependency by holding group read lock over device
>   open/close and put the onus on the driver to obtain a reference if
>   it will actually use the kvm pointer.  Document the requirement,
>   use lockdep_assert to ensure lock is held during register_notifer;
>   today all callers are from driver open_device. 
> 
> Matthew Rosato (1):
>   vfio: remove VFIO_GROUP_NOTIFY_SET_KVM
> 
>  drivers/gpu/drm/i915/gvt/gtt.c        |  4 +-
>  drivers/gpu/drm/i915/gvt/gvt.h        |  3 -
>  drivers/gpu/drm/i915/gvt/kvmgt.c      | 82 ++++++--------------------
>  drivers/s390/crypto/vfio_ap_ops.c     | 35 ++---------
>  drivers/s390/crypto/vfio_ap_private.h |  3 -
>  drivers/vfio/vfio.c                   | 83 ++++++++++-----------------
>  include/linux/vfio.h                  |  6 +-
>  7 files changed, 57 insertions(+), 159 deletions(-)

Applied to vfio next branch for v5.19.  Thanks,

Alex