arm64: Fix the kernel panic() on QDF2400 platform

[Manoj Iyer]

Tested on Ubuntu 17.04 (Linux 4.10). I am able to boot the kernel on 
QDF2400 platform without any panics.

Tested-by: Manoj Iyer <manoj.iyer at canonical.com>

--
============================
Manoj Iyer
Ubuntu/Canonical
ARM Servers - Cloud
============================

On Wed, 22 Feb 2017, Shanker Donthineni wrote:

> The commit 38fd94b0 'arm64: Work around Falkor erratum 1003' has
> been added to fix the hardware bug but causing a system crash.
> The value of the register x1 which contains 'struct mm_struct *'
> should be preserved inside macro pre_ttbr0_update_workaround.
>
> Macro pre_ttbr0_update_workaround expects 2nd and 3rd arguments
> are temporary registers. Don't clobber register x1, Otherwise
> the next load operation 'mmid x1 x1' access the invalid address.
>
> [<ffff0000080989a0>] cpu_do_switch_mm+0x20/0x40
> [<ffff000008b18614>] efi_virtmap_load+0x34/0x40
> [<ffff000008b1812c>] virt_efi_get_next_variable+0x64/0xc8
> [<ffff000008b16204>] efivar_init+0x8c/0x348
> [<ffff0000092b777c>] efisubsys_init+0xd4/0x270
> [<ffff000009270c74>] do_one_initcall+0x80/0x110
> [<ffff000009270ea0>] kernel_init_freeable+0x19c/0x240
> [<ffff000008d8cef0>] kernel_init+0x10/0x100
> [<ffff000008082ec0>] ret_from_fork+0x10/0x50
> Code: d5033fdf b340bc01 d5182001 d5033fdf (f9416821)
> ---[ end trace 15247ca922eb6bb7 ]---
> note: swapper/0[1] exited with preempt_count 2
> Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>
> SMP: stopping secondary CPUs
> ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
>
> Signed-off-by: Shanker Donthineni <shankerd at codeaurora.org>
> ---
> arch/arm64/mm/proc.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
> index cd4d53d..877d42f 100644
> --- a/arch/arm64/mm/proc.S
> +++ b/arch/arm64/mm/proc.S
> @@ -138,7 +138,7 @@ ENDPROC(cpu_do_resume)
>  *	- pgd_phys - physical address of new TTB
>  */
> ENTRY(cpu_do_switch_mm)
> -	pre_ttbr0_update_workaround x0, x1, x2
> +	pre_ttbr0_update_workaround x0, x2, x3
> 	mmid	x1, x1				// get mm->context.id
> 	bfi	x0, x1, #48, #16		// set the ASID
> 	msr	ttbr0_el1, x0			// set TTBR0
>