linux-kernel - RE: [PATCH] vfio: fix deadlock between group lock and kvm lock

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Message-ID: <BN9PR11MB5276E39EE37A7BA2E1B896278CD19@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 1 Feb 2023 06:13:11 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "jgg@...dia.com" <jgg@...dia.com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "farman@...ux.ibm.com" <farman@...ux.ibm.com>,
        "pmorel@...ux.ibm.com" <pmorel@...ux.ibm.com>,
        "borntraeger@...ux.ibm.com" <borntraeger@...ux.ibm.com>,
        "frankja@...ux.ibm.com" <frankja@...ux.ibm.com>,
        "imbrenda@...ux.ibm.com" <imbrenda@...ux.ibm.com>,
        "david@...hat.com" <david@...hat.com>,
        "akrowiak@...ux.ibm.com" <akrowiak@...ux.ibm.com>,
        "jjherne@...ux.ibm.com" <jjherne@...ux.ibm.com>,
        "pasic@...ux.ibm.com" <pasic@...ux.ibm.com>,
        "zhenyuw@...ux.intel.com" <zhenyuw@...ux.intel.com>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] vfio: fix deadlock between group lock and kvm lock

> From: Matthew Rosato <mjrosato@...ux.ibm.com>
> Sent: Wednesday, February 1, 2023 4:07 AM
> 
> -	device->kvm = kvm;
> +	/*
> +	 * Get the KVM pointer currently associated with the group, if there
> +	 * is one, and obtain a reference now that will be held until the
> +	 * open_count reaches 0.  Save the pointer in the device for use by
> +	 * drivers.
> +	 */
> +	spin_lock_irqsave(&group->kvm_ref_lock, flags);
> +	if (group->kvm && vfio_kvm_get_kvm_safe(device, group->kvm))
> +		device->kvm = group->kvm;
> +	spin_unlock_irqrestore(&group->kvm_ref_lock, flags);
> +

No group reference in vfio_main.c. 

btw Yi, looks the deadlock issue also exists in your cdev work.

kvm_vfio_release() holds kvm lock and then try to acquire
device->device_set->lock in vfio_device_file_set_kvm().

vfio_device_ioctl_bind_iommufd() holds device->device_set->lock
and then call vfio_device_open() which finally hit kvm lock
acquisition in driver's open_device routine (e.g. vfio-ap).

A similar fix is required in your series.

Thanks
Kevin