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powerpc/64: Simplify __secondary_start paca->kstack handling

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In __secondary_start() we load the thread_info of the idle task of the
secondary CPU from current_set[cpu], and then convert it into a stack
pointer before storing that back to paca->kstack.

As pointed out in commit f761622e59 ("powerpc: Initialise
paca->kstack before early_setup_secondary") it's important that we
initialise paca->kstack before calling the MMU setup code, in
particular slb_initialize(), because it will bolt the SLB entry for
the kstack into the SLB.

However we have already setup paca->kstack in cpu_idle_thread_init(),
since commit 3b5750644b ("[POWERPC] Bolt in SLB entry for kernel
stack on secondary cpus") (May 2008).

It's also in cpu_idle_thread_init() that we initialise current_set[cpu]
with the thread_info pointer, so there is no issue of the timing being
different between the two.

Therefore the initialisation of paca->kstack in __setup_secondary() is
completely redundant, so remove it.

This has the added benefit of removing code that runs in real mode,
and is therefore restricted by the RMO, and so opens the way for us to
enable THREAD_INFO_IN_TASK.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Michael Ellerman 2019-02-22 23:58:21 +11:00
parent e7fda7e569
commit eafd825ed7
1 changed files with 9 additions and 11 deletions
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20
arch/powerpc/kernel/head_64.S
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@ -801,21 +801,19 @@ __secondary_start:
/* Set thread priority to MEDIUM */ /* Set thread priority to MEDIUM */
HMT_MEDIUM HMT_MEDIUM
/* Initialize the kernel stack */ /*
LOAD_REG_ADDR(r3, current_set) * Do early setup for this CPU, in particular initialising the MMU so we
sldi r28,r24,3 /* get current_set[cpu#] */ * can turn it on below. This is a call to C, which is OK, we're still
ldx r14,r3,r28 * running on the emergency stack.
addi r14,r14,THREAD_SIZE-STACK_FRAME_OVERHEAD */
std r14,PACAKSAVE(r13)
/* Do early setup for that CPU (SLB and hash table pointer) */
bl early_setup_secondary bl early_setup_secondary
/* /*
* setup the new stack pointer, but *don't* use this until * The primary has initialized our kernel stack for us in the paca, grab
* translation is on. * it and put it in r1. We must *not* use it until we turn on the MMU
* below, because it may not be inside the RMO.
*/ */
mr r1, r14 ld r1, PACAKSAVE(r13)
/* Clear backchain so we get nice backtraces */ /* Clear backchain so we get nice backtraces */
li r7,0 li r7,0