kvm.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Farhan Ali <alifm@linux.ibm.com>
To: Halil Pasic <pasic@linux.ibm.com>
Cc: Cornelia Huck <cohuck@redhat.com>,
	farman@linux.ibm.com, linux-s390@vger.kernel.org,
	kvm@vger.kernel.org
Subject: Re: [RFC v2 4/5] vfio-ccw: Don't call cp_free if we are processing a channel program
Date: Tue, 9 Jul 2019 17:27:47 -0400	[thread overview]
Message-ID: <87f7a37f-cc34-36fb-3a33-309e33bbbdde@linux.ibm.com> (raw)
In-Reply-To: <20190709162142.789dd605.pasic@linux.ibm.com>



On 07/09/2019 10:21 AM, Halil Pasic wrote:
> On Tue, 9 Jul 2019 09:46:51 -0400
> Farhan Ali <alifm@linux.ibm.com> wrote:
> 
>>
>>
>> On 07/09/2019 06:16 AM, Cornelia Huck wrote:
>>> On Mon,  8 Jul 2019 16:10:37 -0400
>>> Farhan Ali <alifm@linux.ibm.com> wrote:
>>>
>>>> There is a small window where it's possible that we could be working
>>>> on an interrupt (queued in the workqueue) and setting up a channel
>>>> program (i.e allocating memory, pinning pages, translating address).
>>>> This can lead to allocating and freeing the channel program at the
>>>> same time and can cause memory corruption.
>>>>
>>>> Let's not call cp_free if we are currently processing a channel program.
>>>> The only way we know for sure that we don't have a thread setting
>>>> up a channel program is when the state is set to VFIO_CCW_STATE_CP_PENDING.
>>>
>>> Can we pinpoint a commit that introduced this bug, or has it been there
>>> since the beginning?
>>>
>>
>> I think the problem was always there.
>>
> 
> I think it became relevant with the async stuff. Because after the async
> stuff was added we start getting solicited interrupts that are not about
> channel program is done. At least this is how I remember the discussion.
> 
>>>>
>>>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>>>> ---
>>>>    drivers/s390/cio/vfio_ccw_drv.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
>>>> index 4e3a903..0357165 100644
>>>> --- a/drivers/s390/cio/vfio_ccw_drv.c
>>>> +++ b/drivers/s390/cio/vfio_ccw_drv.c
>>>> @@ -92,7 +92,7 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
>>>>    		     (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT));
>>>>    	if (scsw_is_solicited(&irb->scsw)) {
>>>>    		cp_update_scsw(&private->cp, &irb->scsw);
>>>> -		if (is_final)
>>>> +		if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING)
> 
> Ain't private->state potentially used by multiple threads of execution?

yes

One of the paths I can think of is a machine check from the host which 
will ultimately call vfio_ccw_sch_event callback which could set state 
to NOT_OPER or IDLE.

> Do we need to use atomic operations or external synchronization to avoid
> this being another gamble? Or am I missing something?

I think we probably should think about atomic operations for 
synchronizing the state (and it could be a separate add on patch?).

But for preventing 2 threads from stomping on the cp the check should be 
enough, unless I am missing something?

> 
>>>>    			cp_free(&private->cp);
>>>>    	}
>>>>    	mutex_lock(&private->io_mutex);
>>>
>>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>>>
>>>
>> Thanks for reviewing.
>>
>> Thanks
>> Farhan
> 
> 

  reply	other threads:[~2019-07-09 21:27 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-08 20:10 [RFC v2 0/5] Some vfio-ccw fixes Farhan Ali
2019-07-08 20:10 ` [RFC v2 1/5] vfio-ccw: Fix misleading comment when setting orb.cmd.c64 Farhan Ali
2019-07-09  9:57   ` Cornelia Huck
2019-07-08 20:10 ` [RFC v2 2/5] vfio-ccw: Fix memory leak and don't call cp_free in cp_init Farhan Ali
2019-07-09 10:06   ` Cornelia Huck
2019-07-09 14:07     ` Farhan Ali
2019-07-09 14:18       ` Cornelia Huck
2019-07-08 20:10 ` [RFC v2 3/5] vfio-ccw: Set pa_nr to 0 if memory allocation fails for pa_iova_pfn Farhan Ali
2019-07-09 10:08   ` Cornelia Huck
2019-07-08 20:10 ` [RFC v2 4/5] vfio-ccw: Don't call cp_free if we are processing a channel program Farhan Ali
2019-07-09 10:16   ` Cornelia Huck
2019-07-09 13:46     ` Farhan Ali
2019-07-09 14:21       ` Halil Pasic
2019-07-09 21:27         ` Farhan Ali [this message]
2019-07-10 13:45           ` Cornelia Huck
2019-07-10 16:10             ` Farhan Ali
2019-07-11 12:28               ` Eric Farman
2019-07-11 14:57           ` Halil Pasic
2019-07-11 20:09             ` Eric Farman
2019-07-12 13:59               ` Halil Pasic
2019-07-08 20:10 ` [RFC v2 5/5] vfio-ccw: Update documentation for csch/hsch Farhan Ali
2019-07-09 10:14   ` Cornelia Huck
2019-07-09 12:47     ` Farhan Ali

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:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

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

  git send-email \
    --in-reply-to=87f7a37f-cc34-36fb-3a33-309e33bbbdde@linux.ibm.com \
    --to=alifm@linux.ibm.com \
    --cc=cohuck@redhat.com \
    --cc=farman@linux.ibm.com \
    --cc=kvm@vger.kernel.org \
    --cc=linux-s390@vger.kernel.org \
    --cc=pasic@linux.ibm.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* 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).