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

Eric Farman
2019-06-18T20:24:02Z

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);
- 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;
--
2.17.1