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powerpc/kernel: Avoid memory corruption at early stage

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When calling to early_setup(), we pick "boot_paca" up for the master CPU
and initialize that with initialise_paca(). At that point, the SLB
shadow buffer isn't populated yet. Updating the SLB shadow buffer should
corrupt what we had in physical address 0 where the trap instruction is
usually stored.

This hasn't been observed to cause any trouble in practice, but is
obviously fishy.

Fixes: 6f4441ef7009 ("powerpc: Dynamically allocate slb_shadow from memblock")
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Gavin Shan 2015-01-08 16:40:51 +11:00 committed by Michael Ellerman
parent 53a448c3d5
commit 6f20e7f2e9
1 changed files with 8 additions and 0 deletions
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8
arch/powerpc/kernel/paca.c
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@ -115,6 +115,14 @@ static struct slb_shadow * __init init_slb_shadow(int cpu)
{
struct slb_shadow *s = &slb_shadow[cpu];
/*
* When we come through here to initialise boot_paca, the slb_shadow
* buffers are not allocated yet. That's OK, we'll get one later in
* boot, but make sure we don't corrupt memory at 0.
*/
if (!slb_shadow)
return NULL;
s->persistent = cpu_to_be32(SLB_NUM_BOLTED);
s->buffer_length = cpu_to_be32(sizeof(*s));