linux-kernel - Re: [Xen-devel] [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down

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: <55A56B48.4060605@oracle.com>
Date:	Tue, 14 Jul 2015 16:04:24 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	Joerg Roedel <jroedel@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Peter Anvin <hpa@...or.com>,
	xen-devel <xen-devel@...ts.xenproject.org>,
	Borislav Petkov <bp@...e.de>, xiao jin <jin.xiao@...el.com>
Subject: Re: [Xen-devel] [patch 1/4] hotplug: Prevent alloc/free of irq descriptors
 during cpu up/down

On 07/14/2015 01:32 PM, Thomas Gleixner wrote:
> On Tue, 14 Jul 2015, Boris Ostrovsky wrote:
>> On 07/14/2015 11:44 AM, Thomas Gleixner wrote:
>>> On Tue, 14 Jul 2015, Boris Ostrovsky wrote:
>>>>> Prevent allocation and freeing of interrupt descriptors accross cpu
>>>>> hotplug.
>>>> This breaks Xen guests that allocate interrupt descriptors in .cpu_up().
>>> And where exactly does XEN allocate those descriptors?
>> xen_cpu_up()
>>      xen_setup_timer()
>>          bind_virq_to_irqhandler()
>>              bind_virq_to_irq()
>>                  xen_allocate_irq_dynamic()
>>                      xen_allocate_irqs_dynamic()
>>                          irq_alloc_descs()
>>
>>
>> There is also a similar pass via xen_cpu_up() -> xen_smp_intr_init()
> Sigh.
>   
>>>    
>>>> Any chance this locking can be moved into arch code?
>>> No.
> The issue here is that all architectures need that protection and just
> Xen does irq allocations in cpu_up.
>
> So moving that protection into architecture code is not really an
> option.
>
>>>> Otherwise we will need to have something like arch_post_cpu_up()
>>>> after the lock is released.
> I'm not sure, that this will work. You probably want to do this in the
> cpu prepare stage, i.e. before calling __cpu_up().



For PV guests (the ones that use xen_cpu_up()) it will work either 
before or after __cpu_up(). At least my (somewhat limited) testing 
didn't show any problems so far.

However, HVM CPUs use xen_hvm_cpu_up() and if you read comments there 
you will see that xen_smp_intr_init() needs to be called before 
native_cpu_up() but xen_init_lock_cpu() (which eventually calls 
irq_alloc_descs()) needs to be called after.

I think I can split xen_init_lock_cpu() so that the part that needs to 
be called after will avoid going into irq core code. And then the rest 
will go into arch_cpu_prepare().


-boris
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/