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

Farhan Ali
2019-06-19T20:13:36Z

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;
>