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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9b6c0c4d-57c9-6a9a-379e-82f073b73988@linux.ibm.com>
Date:   Wed, 1 Feb 2023 09:27:45 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     "Tian, Kevin" <kevin.tian@...el.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

On 2/1/23 1:13 AM, Tian, Kevin wrote:
>> 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. 

OK -- I think to do that I'll have to move the lock/unlock of the dev_set lock to group.c right before we call vfio_device_{open,close} and check open_count there to make decisions about the kvm ref (before calling vfio_device_open to decide to get kvm ref, after returning from vfio_device_open to see if we to drop ref on error, after close to see if we need to drop ref).

> 
> 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