[RFC PATCH 0/2] dm-crypt support for per-sector NVMe metadata

[Mikulas Patocka]

On Mon, 27 May 2024, Eric Wheeler wrote:

> On Wed, 15 May 2024, Mikulas Patocka wrote:
> > Hi
> > 
> > Some NVMe devices may be formatted with extra 64 bytes of metadata per 
> > sector.
> > 
> > Here I'm submitting for review dm-crypt patches that make it possible to 
> > use per-sector metadata for authenticated encryption. With these patches, 
> > dm-crypt can run directly on the top of a NVMe device, without using 
> > dm-integrity. These patches increase write throughput twice, because there 
> > is no write to the dm-integrity journal.
> > 
> > An example how to use it (so far, there is no support in the userspace 
> > cryptsetup tool):
> > 
> > # nvme format /dev/nvme1 -n 1 -lbaf=4
> > # dmsetup create cr --table '0 1048576 crypt 
> > capi:authenc(hmac(sha256),cbc(aes))-essiv:sha256 
> > 01b11af6b55f76424fd53fb66667c301466b2eeaf0f39fd36d26e7fc4f52ade2de4228e996f5ae2fe817ce178e77079d28e4baaebffbcd3e16ae4f36ef217298 
> > 0 /dev/nvme1n1 0 2 integrity:32:aead sector_size:4096'
> 
> Thats really an amazing feature, and I think your implementation is simple 
> and elegant.  Somehow reminds me of 520/528-byte sectors that big 
> commercial filers use, but in a way the Linux could use.
> 
> Questions:
> 
> - I see you are using 32-bytes of AEAD data (out of 64).  Is AEAD always 
>   32-bytes, or can it vary by crypto mechanism?

It varies. I.e. if you use hmac(sha512), full 64 bytes will be used.

> - What drive are you using?

Western Digital SN840

WUS4BA119DSP3X3

> I am curious what your `nvme id-ns` output 
>   looks like. Do you have 64 in the `ms` value?
> 
>         # nvme id-ns /dev/nvme0n1 | grep lbaf
>         nlbaf   : 0
>         nulbaf  : 0
>         lbaf  0 : ms:0   lbads:9  rp:0 (in use)
>                      ^         ^512b

Yes, I have this:
lbaf  0 : ms:0   lbads:9  rp:0
lbaf  1 : ms:8   lbads:9  rp:0
lbaf  2 : ms:0   lbads:12 rp:0
lbaf  3 : ms:8   lbads:12 rp:0
lbaf  4 : ms:64  lbads:12 rp:0 (in use)

Mikulas

> --
> Eric Wheeler