Quick summary: on i386, 4 modules are aliased to 'aes': padlock-aes, geode-aes,
aes-i586, and aes_generic. I need at least one of those to decrypt my root
filesystem. In kernel 2.6.25-rc1 padlock-aes now returns an error when you
attempt to insert it, so modprobe gives up on the other 3, leaving me without
AES (and thus unable to boot).

The long version:

My rawhide machine - which is using a LUKS encrypted LVM PV for its root - is
unbootable with any 2.6.25 kernel. It requests the key and then fails to unlock
the device:

device-mapper: table: 253:0: crypt: Error allocating crypto tfm
device-mapper: ioctl: error adding target to table
device-mapper: ioctl: device doesn't appear to be in the dev hash table.
Failed to setup dm-crypt key mapping. 
Check kernel for support for the aes-cbc-essiv:sha256 cipher spec and verify
that /dev/sda2 contains at least 133 sectors.

So it would seem we've failed to load the cipher module(s). Scrolling back up, I
see:
padlock: VIA PadLock not detected.
WARNING: Error inserting padlock_aes ($modpath/padlock-aes.ko): No such device
padlock: VIA PadLock Hash Engine not detected.
WARNING: Error inserting padlock_sha ($modpath/padlock-sha.ko): No such device

With kernel 2.6.24.1-31 and  2.6.24-2 (which work), these error messages don't
appear, and the system boots normally. 

LUKS needs at least one AES module to decrypt my root filesystem. 'modprobe
aes', in the 2.6.24 kernels, installs all the modules which are aliased to
'aes': padlock-aes, geode-aes, aes-i586, aes_generic. 

In 2.6.24 kernels they all probe successfully. With 2.6.25-rc1, inserting the
padlock-aes module now returns an error if you don't have that hardware. I'm
guessing that modprobe gives up at that point, and that's why the message
indicating missing support for aes-cbc-essiv:sha256 appears - no AES modules
were loaded