linux-kernel - Re: [PATCH 1/2] vfio: ccw: bypass bad idaw address when fetching IDAL ccws

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Date:   Mon, 16 Oct 2017 11:09:37 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     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,
        pasic@...ux.vnet.ibm.com, pmorel@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/2] vfio: ccw: bypass bad idaw address when fetching
 IDAL ccws

On Wed, 11 Oct 2017 04:38:21 +0200
Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com> wrote:

> We currently returns the same error code (-EFAULT) to indicate two

s/returns/return/

> different error cases:
> 1. a bug in vfio-ccw implementation has been found.
> 2. a buggy channel program has been detected.
> 
> This brings difficulty for userland program (specifically Qemu) to
> handle.
> 
> Let's use -EFAULT to only indicate the first case. For the second
> case, we simply hand over the ccws to lower level for further
> handling.
> 
> Notice:
> Once a bad idaw address is detected, the current behavior is to
> suppress the ssch. With this fix, the channel program will be
> accepted, and partial of the channel program (the part ahead of

s/partial/part/

> the bad idaw) could possibly be executed by the device before
> I/O conclusion.

That actually sounds more sensible than the current behaviour.

I'll fix up the typos when applying.

> 
> Suggested-by: Halil Pasic <pasic@...ux.vnet.ibm.com>
> Reviewed-by: Pierre Morel <pmorel@...ux.vnet.ibm.com>
> Signed-off-by: Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com>
> ---
>  drivers/s390/cio/vfio_ccw_cp.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> index 5ccfdc80d0ec..722f8b8c7273 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.c
> +++ b/drivers/s390/cio/vfio_ccw_cp.c
> @@ -569,10 +569,6 @@ static int ccwchain_fetch_idal(struct ccwchain *chain,
>  
>  	for (i = 0; i < idaw_nr; i++) {
>  		idaw_iova = *(idaws + i);
> -		if (IS_ERR_VALUE(idaw_iova)) {
> -			ret = -EFAULT;
> -			goto out_free_idaws;
> -		}
>  
>  		ret = pfn_array_alloc_pin(pat->pat_pa + i, cp->mdev,
>  					  idaw_iova, 1);