linux-kernel - Re: [PATCH v7 09/11] vfio: Delete the unbound

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Date:   Mon, 28 Feb 2022 15:06:28 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Dan Williams <dan.j.williams@...el.com>, rafael@...nel.org,
        Diana Craciun <diana.craciun@....nxp.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Stuart Yoder <stuyoder@...il.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Li Yang <leoyang.li@....com>,
        Dmitry Osipenko <digetx@...il.com>,
        iommu@...ts.linux-foundation.org, linux-pci@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 09/11] vfio: Delete the unbound_list

On Mon, 28 Feb 2022 08:50:54 +0800
Lu Baolu <baolu.lu@...ux.intel.com> wrote:

> From: Jason Gunthorpe <jgg@...dia.com>
> 
> commit 60720a0fc646 ("vfio: Add device tracking during unbind") added the
> unbound list to plug a problem with KVM where KVM_DEV_VFIO_GROUP_DEL
> relied on vfio_group_get_external_user() succeeding to return the
> vfio_group from a group file descriptor. The unbound list allowed
> vfio_group_get_external_user() to continue to succeed in edge cases.
> 
> However commit 5d6dee80a1e9 ("vfio: New external user group/file match")
> deleted the call to vfio_group_get_external_user() during
> KVM_DEV_VFIO_GROUP_DEL. Instead vfio_external_group_match_file() is used
> to directly match the file descriptor to the group pointer.
> 
> This in turn avoids the call down to vfio_dev_viable() during
> KVM_DEV_VFIO_GROUP_DEL and also avoids the trouble the first commit was
> trying to fix.
> 
> There are no other users of vfio_dev_viable() that care about the time
> after vfio_unregister_group_dev() returns, so simply delete the
> unbound_list entirely.
> 
> Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>
> Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/vfio/vfio.c | 74 ++-------------------------------------------
>  1 file changed, 2 insertions(+), 72 deletions(-)

Acked-by: Alex Williamson <alex.williamson@...hat.com>