cryptsetup benchmark --cipher aes-xts
    # Tests are approximate using memory only (no storage IO).
    #  Algorithm | Key |  Encryption |  Decryption
         aes-xts   256b  2266.2 MiB/s  2273.8 MiB/s

perf says

    21.86%  cryptsetup  [aesni_intel]           [k] _aesni_dec4                       
    19.83%  cryptsetup  [aesni_intel]           [k] _aesni_enc4                       
    17.80%  cryptsetup  [aesni_intel]           [k] aesni_xts_crypt8                  
    13.73%  cryptsetup  [kernel]                [k] copy_user_generic_unrolled        
     2.20%  cryptsetup  [kernel]                [k] get_page_from_freelist            
     1.86%  cryptsetup  [glue_helper]           [k] glue_xts_crypt_128bit             
     1.53%  cryptsetup  [kernel]                [k] put_page                          
     1.36%  cryptsetup  [kernel]                [k] blkcipher_walk_done               

so it's using the code from:

https://github.com/torvalds/linux/blob/master/arch/x86/crypt...

I don't know if using AVX would speed it up. openssl is faster (openssl speed -evp aes-256-gcm and aes-256-xts).