On 6/19/19 4:13 PM, Farhan Ali wrote:
>
>
> 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@xxxxxxxxxx>
>> Signed-off-by: Eric Farman <farman@xxxxxxxxxxxxx>
>> ---
>> 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?
Yeah, they'll be garbage there, but I'm not sure it's a problem. By the
time we get here again (ccwchain_loop_tic() -> ccwchain_handle_ccw()),
we'll have saved the relevant CCWs for the first segment. And the
second time through we'll be copying a fresh 2K from the target of the
TIC to cp->guest_cp, overwriting all that stale data with new CCWs (and
new garbage data).
>
>
>> - 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;
>>
