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] [day] [month] [year] [list]

Date:   Thu, 2 Feb 2023 03:08:51 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "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>,
        "Tian, Kevin" <kevin.tian@...el.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 10:43 PM
> 
> On 2/1/23 7:43 AM, Liu, Yi L wrote:
> >> From: Jason Gunthorpe <jgg@...dia.com>
> >> Sent: Wednesday, February 1, 2023 4:26 AM
> >>
> >> On Tue, Jan 31, 2023 at 03:06:35PM -0500, Matthew Rosato wrote:
> >>> @@ -799,13 +794,14 @@
> >> EXPORT_SYMBOL_GPL(vfio_file_enforced_coherent);
> >>>  void vfio_file_set_kvm(struct file *file, struct kvm *kvm)
> >>>  {
> >>>  	struct vfio_group *group = file->private_data;
> >>> +	unsigned long flags;
> >>>
> >>>  	if (!vfio_file_is_group(file))
> >>>  		return;
> >>>
> >>> -	mutex_lock(&group->group_lock);
> >>> +	spin_lock_irqsave(&group->kvm_ref_lock, flags);
> >>>  	group->kvm = kvm;
> >>> -	mutex_unlock(&group->group_lock);
> >>> +	spin_unlock_irqrestore(&group->kvm_ref_lock, flags);
> >>
> >> We know we are in a sleeping context here so these are just
> >> 'spin_lock()', same with the other one
> >
> > a dumb question. Why spinlock is required here? 😊
> >
> 
> You mean as opposed to another mutex?  I don't think it's required per se
> (we are replacing a mutex so we could have again used another mutex
> here), but all current users of this new lock hold it over a very short window
> (e.g. set a pointer as above, or refcount++ and copy the pointer as in the
> first device_open)

I see. Just not sure if spinlock is required for a special reason.

Regards,
Yi Liu