1) If remaining ring space before the end of the ring is
smaller then the next cmd to write, tcmu writes a padding
entry which fills the remaining space at the end of the
ring.
Then tcmu calls tcmu_flush_dcache_range() with the size
of struct tcmu_cmd_entry as data length to flush.
If the space filled by the padding was smaller then
tcmu_cmd_entry, tcmu_flush_dcache_range() is called for
an address range reaching behind the end of the vmalloc'ed
ring.
tcmu_flush_dcache_range() in a loop calls
flush_dcache_page(virt_to_page(start));
for every page being part of the range. On x86 the line is
optimized out by the compiler, as flush_dcache_page() is
empty on x86.
But I assume the above can cause trouble on other
architectures that really have a flush_dcache_page().
For paddings only the header part of an entry is relevant
Due to alignment rules the header always fits in the
remaining space, if padding is needed.
So tcmu_flush_dcache_range() can safely be called with
sizeof(entry->hdr) as the length here.
2) After it has written a command to cmd ring, tcmu calls
tcmu_flush_dcache_range() using the size of a struct
tcmu_cmd_entry as data length to flush.
But if a command needs many iovecs, the real size of the
command may be bigger then tcmu_cmd_entry, so a part of
the written command is not flushed then.
Signed-off-by: Bodo Stroesser <bstroesser@xxxxxxxxxxxxxx>
---
drivers/target/target_core_user.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c
index f769bb1e3735..cdb4848d23c6 100644
--- a/drivers/target/target_core_user.c
+++ b/drivers/target/target_core_user.c
@@ -1026,7 +1026,7 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
entry->hdr.cmd_id = 0; /* not used for PAD */
entry->hdr.kflags = 0;
entry->hdr.uflags = 0;
- tcmu_flush_dcache_range(entry, sizeof(*entry));
+ tcmu_flush_dcache_range(entry, sizeof(entry->hdr));
UPDATE_HEAD(mb->cmd_head, pad_size, udev->cmdr_size);
tcmu_flush_dcache_range(mb, sizeof(*mb));
@@ -1084,7 +1084,7 @@ static int queue_cmd_ring(struct tcmu_cmd *tcmu_cmd, sense_reason_t *scsi_err)
cdb_off = CMDR_OFF + cmd_head + base_command_size;
memcpy((void *) mb + cdb_off, se_cmd->t_task_cdb, scsi_command_size(se_cmd->t_task_cdb));
entry->req.cdb_off = cdb_off;
- tcmu_flush_dcache_range(entry, sizeof(*entry));
+ tcmu_flush_dcache_range(entry, command_size);
UPDATE_HEAD(mb->cmd_head, command_size, udev->cmdr_size);
tcmu_flush_dcache_range(mb, sizeof(*mb));
--
2.12.3
