Re: [RFC PATCH v1 1/5] vfio-ccw: Move guest_cp storage into common struct

[Farhan Ali <alifm@linux.ibm.com>]

On 06/18/2019 04:23 PM, Eric Farman wrote:
> Rather than allocating/freeing a piece of memory every time
> we try to figure out how long a CCW chain is, let's use a piece
> of memory allocated for each device.
> 
> The io_mutex added with commit 4f76617378ee9 ("vfio-ccw: protect
> the I/O region") is held for the duration of the VFIO_CCW_EVENT_IO_REQ
> event that accesses/uses this space, so there should be no race
> concerns with another CPU attempting an (unexpected) SSCH for the
> same device.
> 
> Suggested-by: Cornelia Huck <cohuck@redhat.com>
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
> Conny, your suggestion [1] did not go unnoticed.  :)
> 
> [1] https://patchwork.kernel.org/comment/22312659/
> ---
>   drivers/s390/cio/vfio_ccw_cp.c  | 23 ++++-------------------
>   drivers/s390/cio/vfio_ccw_cp.h  |  7 +++++++
>   drivers/s390/cio/vfio_ccw_drv.c |  7 +++++++
>   3 files changed, 18 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> index 90d86e1354c1..f358502376be 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.c
> +++ b/drivers/s390/cio/vfio_ccw_cp.c
> @@ -16,12 +16,6 @@
>   
>   #include "vfio_ccw_cp.h"
>   
> -/*
> - * Max length for ccw chain.
> - * XXX: Limit to 256, need to check more?
> - */
> -#define CCWCHAIN_LEN_MAX	256
> -
>   struct pfn_array {
>   	/* Starting guest physical I/O address. */
>   	unsigned long		pa_iova;
> @@ -386,7 +380,7 @@ static void ccwchain_cda_free(struct ccwchain *chain, int idx)
>    */
>   static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
>   {
> -	struct ccw1 *ccw, *p;
> +	struct ccw1 *ccw = cp->guest_cp;
>   	int cnt;
>   
>   	/*
> @@ -394,15 +388,9 @@ static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
>   	 * Currently the chain length is limited to CCWCHAIN_LEN_MAX (256).
>   	 * So copying 2K is enough (safe).
>   	 */
> -	p = ccw = kcalloc(CCWCHAIN_LEN_MAX, sizeof(*ccw), GFP_KERNEL);
> -	if (!ccw)
> -		return -ENOMEM;
> -
>   	cnt = copy_ccw_from_iova(cp, ccw, iova, CCWCHAIN_LEN_MAX);

Just a minor concern, should we clear out cp->guest_cp memory before we 
do the copying? Given that the ccwchain_calc_length will also call be 
called during tic handling, it's possible there might be some garbage 
data in guest_cp, no?


> -	if (cnt) {
> -		kfree(ccw);
> +	if (cnt)
>   		return cnt;
> -	}
>   
>   	cnt = 0;
>   	do {
> @@ -413,10 +401,8 @@ static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
>   		 * orb specified one of the unsupported formats, we defer
>   		 * checking for IDAWs in unsupported formats to here.
>   		 */
> -		if ((!cp->orb.cmd.c64 || cp->orb.cmd.i2k) && ccw_is_idal(ccw)) {
> -			kfree(p);
> +		if ((!cp->orb.cmd.c64 || cp->orb.cmd.i2k) && ccw_is_idal(ccw))
>   			return -EOPNOTSUPP;
> -		}
>   
>   		/*
>   		 * We want to keep counting if the current CCW has the
> @@ -435,7 +421,6 @@ static int ccwchain_calc_length(u64 iova, struct channel_program *cp)
>   	if (cnt == CCWCHAIN_LEN_MAX + 1)
>   		cnt = -EINVAL;
>   
> -	kfree(p);
>   	return cnt;
>   }
>   
> @@ -461,7 +446,7 @@ static int ccwchain_handle_ccw(u32 cda, struct channel_program *cp)
>   	struct ccwchain *chain;
>   	int len, ret;
>   
> -	/* Get chain length. */
> +	/* Copy the chain from cda to cp, and count the CCWs in it */
>   	len = ccwchain_calc_length(cda, cp);
>   	if (len < 0)
>   		return len;
> diff --git a/drivers/s390/cio/vfio_ccw_cp.h b/drivers/s390/cio/vfio_ccw_cp.h
> index 3c20cd208da5..7cdc38049033 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.h
> +++ b/drivers/s390/cio/vfio_ccw_cp.h
> @@ -16,6 +16,12 @@
>   
>   #include "orb.h"
>   
> +/*
> + * Max length for ccw chain.
> + * XXX: Limit to 256, need to check more?
> + */
> +#define CCWCHAIN_LEN_MAX	256
> +
>   /**
>    * struct channel_program - manage information for channel program
>    * @ccwchain_list: list head of ccwchains
> @@ -32,6 +38,7 @@ struct channel_program {
>   	union orb orb;
>   	struct device *mdev;
>   	bool initialized;
> +	struct ccw1 *guest_cp;
>   };
>   
>   extern int cp_init(struct channel_program *cp, struct device *mdev,
> diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
> index 66a66ac1f3d1..34a9a5e3fd36 100644
> --- a/drivers/s390/cio/vfio_ccw_drv.c
> +++ b/drivers/s390/cio/vfio_ccw_drv.c
> @@ -129,6 +129,11 @@ static int vfio_ccw_sch_probe(struct subchannel *sch)
>   	if (!private)
>   		return -ENOMEM;
>   
> +	private->cp.guest_cp = kcalloc(CCWCHAIN_LEN_MAX, sizeof(struct ccw1),
> +				       GFP_KERNEL);
> +	if (!private->cp.guest_cp)
> +		goto out_free;
> +
>   	private->io_region = kmem_cache_zalloc(vfio_ccw_io_region,
>   					       GFP_KERNEL | GFP_DMA);
>   	if (!private->io_region)
> @@ -169,6 +174,7 @@ static int vfio_ccw_sch_probe(struct subchannel *sch)
>   		kmem_cache_free(vfio_ccw_cmd_region, private->cmd_region);
>   	if (private->io_region)
>   		kmem_cache_free(vfio_ccw_io_region, private->io_region);
> +	kfree(private->cp.guest_cp);
>   	kfree(private);
>   	return ret;
>   }
> @@ -185,6 +191,7 @@ static int vfio_ccw_sch_remove(struct subchannel *sch)
>   
>   	kmem_cache_free(vfio_ccw_cmd_region, private->cmd_region);
>   	kmem_cache_free(vfio_ccw_io_region, private->io_region);
> +	kfree(private->cp.guest_cp);
>   	kfree(private);
>   
>   	return 0;
>