Re: [PATCH 4/4] block: Integrity profile init function to trigger module loads

Hi Ard,

quoted

However, since the dependency for "crc10dif" is already satisfied,
nothing is going to cause the hardware-accelerated kernel modules to
get loaded.

This is not true. All accelerated implementations based on SIMD
polynomial multiplication are tried to the respective CPU features
bits. This applies to x86, power, ARM and arm64.

E.g., for x86 you have

alias:          cpu:type:x86,ven*fam*mod*:feature:*0081*

which will be matched by udev if /sys/devices/system/cpu/modalias
contains feature 0081, and so the modules will be loaded automatically
at boot.

If I can avoid carrying that init callback in the block integrity code
that will definitely make me happy. However, loading crct10dif-pclmul
does not happen automatically for me. crc-t10dif is linked statically
and every user of the CRC goes through that library. So nothing ever
requests the "crct10dif" modalias and no accelerator modules are loaded.

<fresh boot>

# lsmod | grep crc
crc32c_intel           24576  0
crc_ccitt              16384  1 ipv6

# modinfo crc32c_intel | grep cpu:type
alias:          cpu:type:x86,ven*fam*mod*:feature:*0094*

# modinfo crct10dif-pclmul | grep cpu:type
alias:          cpu:type:x86,ven*fam*mod*:feature:*0081*

# egrep -o "0081|0094" /sys/devices/system/cpu/modalias
0081
0094

# modprobe crct10dif
# lsmod | grep crc
crct10dif_pclmul       16384  1
crc32c_intel           24576  0
crc_ccitt              16384  1 ipv6

It's interesting that crc32c_intel is loaded but libcrc32c is not. That
matches your description of how things should work. But crct10dif-pclmul
isn't loaded and neither is crc32_pclmul:

# modprobe crc32
# lsmod | grep crc
crc32_generic          16384  0
crc32_pclmul           16384  0
crc32c_intel           24576  0
crc_ccitt              16384  1 ipv6

-- 
Martin K. Petersen	Oracle Linux Engineering

On 26 August 2018 at 15:30, Martin K. Petersen
[off-list ref] wrote:

Hi Ard,

quoted

quoted

However, since the dependency for "crc10dif" is already satisfied,
nothing is going to cause the hardware-accelerated kernel modules to
get loaded.

This is not true. All accelerated implementations based on SIMD
polynomial multiplication are tried to the respective CPU features
bits. This applies to x86, power, ARM and arm64.

E.g., for x86 you have

alias:          cpu:type:x86,ven*fam*mod*:feature:*0081*

which will be matched by udev if /sys/devices/system/cpu/modalias
contains feature 0081, and so the modules will be loaded automatically
at boot.

If I can avoid carrying that init callback in the block integrity code
that will definitely make me happy. However, loading crct10dif-pclmul
does not happen automatically for me. crc-t10dif is linked statically
and every user of the CRC goes through that library. So nothing ever
requests the "crct10dif" modalias and no accelerator modules are loaded.

<fresh boot>

# lsmod | grep crc
crc32c_intel           24576  0
crc_ccitt              16384  1 ipv6

# modinfo crc32c_intel | grep cpu:type
alias:          cpu:type:x86,ven*fam*mod*:feature:*0094*

# modinfo crct10dif-pclmul | grep cpu:type
alias:          cpu:type:x86,ven*fam*mod*:feature:*0081*

# egrep -o "0081|0094" /sys/devices/system/cpu/modalias
0081
0094

# modprobe crct10dif
# lsmod | grep crc
crct10dif_pclmul       16384  1
crc32c_intel           24576  0
crc_ccitt              16384  1 ipv6

It's interesting that crc32c_intel is loaded but libcrc32c is not. That
matches your description of how things should work. But crct10dif-pclmul
isn't loaded and neither is crc32_pclmul:

# modprobe crc32
# lsmod | grep crc
crc32_generic          16384  0
crc32_pclmul           16384  0
crc32c_intel           24576  0
crc_ccitt              16384  1 ipv6

That is odd. On my Ubuntu system, both crct10dif_pclmul and
crc32_pclmul get loaded automatically.