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powerpc/kexec: Fix kexec when using VMX optimised memcpy
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commit b3f271e (powerpc: POWER7 optimised memcpy using VMX and
enhanced prefetch) uses VMX when it is safe to do so (ie not in
interrupt). It also looks at the task struct to decide if we have to
save the current tasks' VMX state.

kexec calls memcpy() at a point where the task struct may have been
overwritten by the new kexec segments. If it has been overwritten
then when memcpy -> enable_altivec looks up current->thread.regs->msr
we get a cryptic oops or lockup.

I also notice we aren't initialising thread_info->cpu, which means
smp_processor_id is broken. Fix that too.

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: <stable@vger.kernel.org> # 3.6+
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Anton Blanchard authored and ozbenh committed May 14, 2013
1 parent 83d5e64 commit 79c66ce
Showing 1 changed file with 4 additions and 0 deletions.
4 changes: 4 additions & 0 deletions arch/powerpc/kernel/machine_kexec_64.c
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
#include <linux/errno.h>
#include <linux/kernel.h>
#include <linux/cpu.h>
#include <linux/hardirq.h>

#include <asm/page.h>
#include <asm/current.h>
Expand Down Expand Up @@ -335,10 +336,13 @@ void default_machine_kexec(struct kimage *image)
pr_debug("kexec: Starting switchover sequence.\n");

/* switch to a staticly allocated stack. Based on irq stack code.
* We setup preempt_count to avoid using VMX in memcpy.
* XXX: the task struct will likely be invalid once we do the copy!
*/
kexec_stack.thread_info.task = current_thread_info()->task;
kexec_stack.thread_info.flags = 0;
kexec_stack.thread_info.preempt_count = HARDIRQ_OFFSET;
kexec_stack.thread_info.cpu = current_thread_info()->cpu;

/* We need a static PACA, too; copy this CPU's PACA over and switch to
* it. Also poison per_cpu_offset to catch anyone using non-static
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