OS X and Arch dual-boot on MBP - bootloader error

Question

I have a Macbook Pro 9,2, and I dual-boot OS X and Arch. My main Arch partition is encrypted with an LVM on LUKS setup, and my main OS X partition is encrypted with Firevault 2. I run the vanilla Arch kernel, and I use xfce as my DE. I use refind as my boot manager, and grub as the bootloader for the Arch partition. This setup has worked flawlessly for several months. I update my Arch system once per week, and last Sunday was a large update since xfce got a large overhaul (in terms of program and config files). However, since the update I cannot boot into OS X (I am posting this here instead of an OS X forum since no change occurred to the OS X system so the problem must be with a change to my Arch system).
When I attempt to boot into OS X, I am asked for my password to decrypt the partition, but then I get the following error message:
efiboot loaded from device: Acpi (PNP0A03,0)/Pci(1F12)/SATA(0,0)/HD(Part3.Sig698A
48BA-88E6-471C-9359-AD63C7EEBE74
boot file path: \System\Library\CoreServices\boot.efi
............Read error 0x6
Error loading kernel cache (0x6)
Error: Aborted returned from boot.efi
*Hit any key to continue*
Starting boot.efi
Using load options ''
efiboot loaded from device: Acpi (PNP0A03,0)/Pci(1F12)/SATA(0,0)/HD(Part3.Sig698A
48BA-88E6-471C-9359-AD63C7EEBE74
boot file path: \com.apple.recovery.boot\boot.efi
.............Read error 0x6
Error loading kernel cache (0x6)
Error: Aborted returned from boot.efi
*Hit any key to continue*
When I hit a key, I get taken back to the refind menu. If I choose OS X again, I get the same error. This cycle can be repeated ad nauseam. Booting into my Arch partition, on the other hand, works just fine, with one hiccup. While usability does not seem to be reduced, after I input my password to decrypt the Arch partition, and before I see the tty1 login, I (since Sunday) occasionally get the following error message that I have never had before:
19.636262] [drm:crypt_set_fifo_underrun_reporting] *ERROR* uncleared pch fifo underrun on pch transcoder
19.636264] [drm:crypt_serr_int_handler] *ERROR* PCH transcoder A FIFO underrun
19.331860] ata1.00: exception Emask 0x50 SAct 0x1100 SErr 0x280900 action 0x6 frozen
19.331927] ata1.00: irq_stat 0x08000000, interface fatal error
19.331974] ata1: SError: {UnrecovData HostInt 10B8B BadCRC }
19.332821] ata1.00: failed command: READ FPDMA QUEUED
19.332866] ata1.00: cmd 60/00:40:70:c1:01/01:00:24:00:00/40 tag 8 ncq 131072 in
19.332866] res 40/00:60:b0:55:2a/00:00:24:00:00/40 Emask 0x50 (ATA bus error)
19.332176] ata1.00: status: { DRDY }
The "READ FPDMA QUEUED" line and those below it repeat a few time with different numbers following "cmd" and "res," but then after a few moments the messages clear off the screen and I arrive at my tty1 login screen and from there everything in Arch (including my now-upgraded DE) works normally. This error does not occur during all boots, but I cannot discern any pattern behind when I see it and when I do not. The OS X error and failure to boot occurs every time I try to boot into OS X.
I have learned a lot as an Arch user, but this problem is beyond me. Google has not been particularly friendly, understandably so given the peculiarity of the problem and my setup. I have not yet tried undoing the update I did on Sunday because (a) it would be a pain since there were >30 packages that were upgraded, and (b) I have no evidence that the upgrade was actually causative of this issue, though I may eventually attempt the downgrade out of desperation if I cannot find a solution. Note that the update I keep referencing did not including a kernel update.
I appreciate any advice or insight that you can offer.

Answer 1

I don't have much in the way of a solution for your problem, but to start with, what were the  > 30 packages? In particular, was grub/refind updated (or anything else that would likely touch your efi partition? I know from my own messing with refind, that you can potentially 'damage' your partition layout with certain commands which maybe causing osx not to boot...
Then again, the errors may have nothing to do with your arch installation and maybe indicative of a different problem all together. Normal procedure is at this point is to backup your complete disk (clone/mirror it, read up on how to do that especially with regards to the encryption systems used), and try to diagnose for any problems the mbp maybe having.
You could use an apple rescue cd (that may no longer be available with newer mbp , I have no idea..) or maybe use a different harddisk and install osx there and see if you can get everything running 'normally' thus ruling out any funky errors with the hw.  check apple's recovery options if need be.
I guess you'll just have to fiddle about a bit and try to more closely determine what the actual problem is. and again, backup your stuff!