Re: [PATCH v2 03/44] x86/asm/head: rename 'stack_start' -> 'initial_stack'

[Brian Gerst]

On Sat, Aug 6, 2016 at 1:25 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> On Fri, Aug 05, 2016 at 11:01:57AM -0500, Josh Poimboeuf wrote:
>> The 8 should be changed to SIZEOF_PTREGS in a later patch
>> ("x86/asm/head: standardize the end of the stack for idle tasks").
>
> But SIZEOF_PTREGS is 21*8. I don't understand.

This patch is only for the boot cpu's idle thread.  All other kernel
threads, including idle threads for the secondary cpus, already have
the pt_regs area reserved.  My best guess for the current 8 byte
padding is to make sure thread_info is calculated properly (by masking
off the low bits from RSP).

Also, this fix should be applied to 32-bit, but make sure to account
for TOP_OF_KERNEL_STACK_PADDING.

--
Brian Gerst