linux-kernel - Re: [PATCH v2 1/5] vfio: ccw: fix cleanup if cp

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Message-Id: <5c23c936-2a13-f514-1c62-aab4031d6dfa@linux.ibm.com>
Date:   Mon, 23 Apr 2018 14:00:11 +0200
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, borntraeger@...ibm.com,
        bjsdjshi@...ux.ibm.com, pmorel@...ux.ibm.com,
        Halil Pasic <pasic@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 1/5] vfio: ccw: fix cleanup if cp_prefetch fails



On 04/23/2018 01:40 PM, Cornelia Huck wrote:
> On Mon, 23 Apr 2018 13:01:09 +0200
> Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com> wrote:
> 
>> From: Halil Pasic <pasic@...ux.vnet.ibm.com>
>>
>> If the translation of a channel program fails, we may end up attempting
>> to clean up (free, unpin) stuff that never got translated (and allocated,
>> pinned) in the first place.
>>
>> By adjusting the lengths of the chains accordingly (so the element that
>> failed, and all subsequent elements are excluded) cleanup activities
>> based on false assumptions can be avoided.
>>
>> Let's make sure cp_free works properly after cp_prefetch returns with an
>> error by setting ch_len of a ccw chain to the number of the translated
>> CCWs on that chain.
> 
> Should that be cc:stable? This problem has been there probably since we
> introduced vfio-ccw, no?
>

Seems emails crossed in flight. Yes I think it should
be cc stable and this was broken since the very beginning.
  
>>
>> Acked-by: Pierre Morel <pmorel@...ux.vnet.ibm.com>
>> Reviewed-by: Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com>
>> Signed-off-by: Halil Pasic <pasic@...ux.vnet.ibm.com>
>> Signed-off-by: Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com>
>> ---
>>   drivers/s390/cio/vfio_ccw_cp.c | 13 ++++++++++++-
>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
>> index 2c7550797ec2..62d66e195304 100644
>> --- a/drivers/s390/cio/vfio_ccw_cp.c
>> +++ b/drivers/s390/cio/vfio_ccw_cp.c
>> @@ -715,6 +715,10 @@ void cp_free(struct channel_program *cp)
>>    * and stores the result to ccwchain list. @cp must have been
>>    * initialized by a previous call with cp_init(). Otherwise, undefined
>>    * behavior occurs.
>> + * For each chain composing the channel program:
>> + * - On entry ch_len holds the count of CCW to be translated.
>> + * - On exit ch_len is adjusted to the count of successfully translated CCW.
>> + * This allows cp_free to find in ch_len the count of CCW to free in a chain.
> 
> s/CCW/CCWs/ (x3)?
> 

Nod.

> Can change on applying.
> 
>>    *
>>    * The S/390 CCW Translation APIS (prefixed by 'cp_') are introduced
>>    * as helpers to do ccw chain translation inside the kernel. Basically
>> @@ -749,11 +753,18 @@ int cp_prefetch(struct channel_program *cp)
>>   		for (idx = 0; idx < len; idx++) {
>>   			ret = ccwchain_fetch_one(chain, idx, cp);
>>   			if (ret)
>> -				return ret;
>> +				goto out_err;
>>   		}
>>   	}
>>   
>>   	return 0;
>> +out_err:
>> +	/* Only cleanup the chain elements that were actually translated. */
>> +	chain->ch_len = idx;
>> +	list_for_each_entry_continue(chain, &cp->ccwchain_list, next) {
>> +		chain->ch_len = 0;
>> +	}
>> +	return ret;
>>   }
>>   
>>   /**
> 
> Else, looks good.
>