xen-devel.lists.xenproject.org archive mirror
 help / color / mirror / Atom feed
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Yanmin Zhang <yanmin_zhang@linux.intel.com>,
	Joerg Roedel <jroedel@suse.de>,
	Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>, Peter Anvin <hpa@zytor.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Borislav Petkov <bp@suse.de>, xiao jin <jin.xiao@intel.com>
Subject: Re: [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down
Date: Tue, 14 Jul 2015 17:07:09 -0400	[thread overview]
Message-ID: <55A579FD.6030000__44993.1169547655$1436908196$gmane$org@oracle.com> (raw)
In-Reply-To: <alpine.DEB.2.11.1507142211390.18576@nanos>

On 07/14/2015 04:15 PM, Thomas Gleixner wrote:
> On Tue, 14 Jul 2015, Boris Ostrovsky wrote:
>> 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().
> I think we should revisit this for 4.3. For 4.2 we can do the trivial
> variant and move the locking in native_cpu_up() and x86 only. x86 was
> the only arch on which such wreckage has been seen in the wild, but we
> should have that protection for all archs in the long run.
> Patch below should fix the issue.

Thanks! Most of my tests passed, I had a couple of failures but I will 
need to see whether they are related to this patch.


  parent reply	other threads:[~2015-07-14 21:08 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20150705170530.849428850@linutronix.de>
     [not found] ` <20150705171102.063519515@linutronix.de>
2015-07-14 14:39   ` [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down Boris Ostrovsky
     [not found]   ` <55A51F10.7010407@oracle.com>
2015-07-14 15:44     ` Thomas Gleixner
     [not found]     ` <alpine.DEB.2.11.1507141743150.18576@nanos>
2015-07-14 16:03       ` Boris Ostrovsky
     [not found]       ` <55A532C2.4080306@oracle.com>
2015-07-14 17:32         ` Thomas Gleixner
     [not found]         ` <alpine.DEB.2.11.1507141901460.18576@nanos>
2015-07-14 20:04           ` Boris Ostrovsky
     [not found]           ` <55A56B48.4060605@oracle.com>
2015-07-14 20:15             ` Thomas Gleixner
     [not found]             ` <alpine.DEB.2.11.1507142211390.18576@nanos>
2015-07-14 21:07               ` Boris Ostrovsky [this message]
     [not found]               ` <55A579FD.6030000@oracle.com>
2016-03-12  9:19                 ` Thomas Gleixner
     [not found]                 ` <alpine.DEB.2.11.1603121017500.3657@nanos>
2016-03-14 13:12                   ` Boris Ostrovsky

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='55A579FD.6030000__44993.1169547655$1436908196$gmane$org@oracle.com' \
    --to=boris.ostrovsky@oracle.com \
    --cc=bp@suse.de \
    --cc=hpa@zytor.com \
    --cc=jin.xiao@intel.com \
    --cc=jroedel@suse.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=xen-devel@lists.xenproject.org \
    --cc=yanmin_zhang@linux.intel.com \


* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).