Clarification needed on use of put_user inside a loop

[Kumar Gaurav]

Hi All,

function put_user() is used to transfer small bytes of data (1-8 byte) 
from kernel space to user space and before transferring, it checks for 
the user's access over that memory area (in user space of-course) using 
function access_ok(). function __put_user() is used for same purpose but 
it skips checking permission part.

Hence when transferring data involves loops then checking permission 
(using access_ok()) once should be good to go then after we can simply 
transfer data using __put_user(), instead of using put_user() itself in 
loop.

I have  found some codes in the driver which use put_user() in loop. Can 
we avoid the overhead of checking the same memory area( where put_user() 
writes) again n again using __put_user() in side loop and checking 
permission using access_ok before entering the loop?

Below is one of the codes I found.
File Name:sound/pci/hda/patch_hdmi.c

Code
-----------
for (i = 0; i < ARRAY_SIZE(channel_allocations); i++, cap++) { //line 
number 1928
                        int chs_bytes = chs * 4;
                        int type = 
spec->ops.chmap_cea_alloc_validate_get_type(cap, chs);
                        unsigned int tlv_chmap[8];

                        if (type < 0)
                                continue;
                        if (size < 8)
                                return -ENOMEM;
                        if (put_user(type, dst) ||
                            put_user(chs_bytes, dst + 1))
                                return -EFAULT;
                        dst += 2;
                        size -= 8;
                        count += 8;
                        if (size < chs_bytes)
                                return -ENOMEM;
                        size -= chs_bytes;
                        count += chs_bytes;
                        spec->ops.cea_alloc_to_tlv_chmap(cap, 
tlv_chmap, chs);
                        if (copy_to_user(dst, tlv_chmap, chs_bytes))
                                return -EFAULT;
                        dst += chs;
                }
---------------------------
Please revert with comment on whether I am correct or not. If yes, I'll 
submit the patches for upgrading codes to skip the overhead of checking 
memory area for permission.

Regards,
Kumar Gaurav
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