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Subject[PATCH 3.16 237/305] xtensa: enable coprocessors that are being flushed
3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Max Filippov <jcmvbkbc@gmail.com>

commit 2958b66694e018c552be0b60521fec27e8d12988 upstream.

coprocessor_flush_all may be called from a context of a thread that is
different from the thread being flushed. In that case contents of the
cpenable special register may not match ti->cpenable of the target
thread, resulting in unhandled coprocessor exception in the kernel
context.
Set cpenable special register to the ti->cpenable of the target register
for the duration of the flush and restore it afterwards.
This fixes the following crash caused by coprocessor register inspection
in native gdb:

(gdb) p/x $w0
Illegal instruction in kernel: sig: 9 [#1] PREEMPT
Call Trace:
___might_sleep+0x184/0x1a4
__might_sleep+0x41/0xac
exit_signals+0x14/0x218
do_exit+0xc9/0x8b8
die+0x99/0xa0
do_illegal_instruction+0x18/0x6c
common_exception+0x77/0x77
coprocessor_flush+0x16/0x3c
arch_ptrace+0x46c/0x674
sys_ptrace+0x2ce/0x3b4
system_call+0x54/0x80
common_exception+0x77/0x77
note: gdb[100] exited with preempt_count 1
Killed

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/xtensa/kernel/process.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/xtensa/kernel/process.c
+++ b/arch/xtensa/kernel/process.c
@@ -83,18 +83,21 @@ void coprocessor_release_all(struct thre

void coprocessor_flush_all(struct thread_info *ti)
{
- unsigned long cpenable;
+ unsigned long cpenable, old_cpenable;
int i;

preempt_disable();

+ RSR_CPENABLE(old_cpenable);
cpenable = ti->cpenable;
+ WSR_CPENABLE(cpenable);

for (i = 0; i < XCHAL_CP_MAX; i++) {
if ((cpenable & 1) != 0 && coprocessor_owner[i] == ti)
coprocessor_flush(ti, i);
cpenable >>= 1;
}
+ WSR_CPENABLE(old_cpenable);

preempt_enable();
}
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