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[PATCH 3.18 32/42] ARC: Re-enable MMU upon Machine Check exception

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3.18-stable review patch.  If anyone has any objections, please let me know.

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

From: Jose Abreu <Jose.Abreu@synopsys.com>

commit 1ee55a8f7f6b7ca4c0c59e0b4b4e3584a085c2d3 upstream.

I recently came upon a scenario where I would get a double fault
machine check exception tiriggered by a kernel module.
However the ensuing crash stacktrace (ksym lookup) was not working
correctly.

Turns out that machine check auto-disables MMU while modules are allocated
in kernel vaddr spapce.

This patch re-enables the MMU before start printing the stacktrace
making stacktracing of modules work upon a fatal exception.

Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Reviewed-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
[vgupta: moved code into low level handler to avoid in 2 places]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arc/kernel/entry.S |    6 ++++++
 arch/arc/mm/tlb.c       |    3 ---
 2 files changed, 6 insertions(+), 3 deletions(-)

--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -315,6 +315,12 @@ ENTRY(EV_MachineCheck)
 	lr  r0, [efa]
 	mov r1, sp
 
+	; hardware auto-disables MMU, re-enable it to allow kernel vaddr
+	; access for say stack unwinding of modules for crash dumps
+	lr	r3, [ARC_REG_PID]
+	or	r3, r3, MMU_ENABLE
+	sr	r3, [ARC_REG_PID]
+
 	lsr  	r3, r2, 8
 	bmsk 	r3, r3, 7
 	brne    r3, ECR_C_MCHK_DUP_TLB, 1f
--- a/arch/arc/mm/tlb.c
+++ b/arch/arc/mm/tlb.c
@@ -689,9 +689,6 @@ void do_tlb_overlap_fault(unsigned long
 
 	local_irq_save(flags);
 
-	/* re-enable the MMU */
-	write_aux_reg(ARC_REG_PID, MMU_ENABLE | read_aux_reg(ARC_REG_PID));
-
 	/* loop thru all sets of TLB */
 	for (set = 0; set < mmu->sets; set++) {
 

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[PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 11/42] [PATCH - RESEND] crypto: AF_ALG - remove SGL terminator indicator when  chaining Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 25/42] scsi: sg: use standard lists for sg_requests Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 03/42] Revert "net: phy: Correctly process PHY_HALTED in phy_stop_machine()" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 42/42] mac80211: flush hw_roc_start work before cancelling the ROC Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 05/42] ipv6: fix memory leak with multiple tables during netns destruction Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 27/42] scsi: sg: factor out sg_fill_request_table() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 12/42] ext4: fix incorrect quotaoff if the quota feature is enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 01/42] ipv6: accept 64k - 1 packet length in ip6_find_1stfragopt() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 21/42] scsi: zfcp: fix payload with full FCP_RSP IU in SCSI trace records Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 29/42] scsi: qla2xxx: Fix an integer overflow in sysfs code Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 08/42] [PATCH] Revert "usb: musb: fix tx fifo flush handling again" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 16/42] skd: Avoid that module unloading triggers a use-after-free Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:30 +0200
  [PATCH 3.18 30/42] ftrace: Fix selftest goto location on error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 07/42] f2fs: check hot_data for roll-forward recovery Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 37/42] bcache: Fix leak of bdev reference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 40/42] bcache: fix for gc and write-back race Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 39/42] bcache: Correct return value for sysfs attach errors Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 41/42] bcache: fix bch_hprint crash and improve output Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 33/42] PCI: shpchp: Enable bridge bus mastering if MSI is enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 06/42] ipv6: fix typo in fib6_net_exit() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 31/42] tracing: Apply trace_clock changes to instance max buffer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 38/42] bcache: correct cache_dirty_target in __update_writeback_rate() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 32/42] ARC: Re-enable MMU upon Machine Check exception Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 28/42] scsi: sg: fixup infoleak when using SG_GET_REQUEST_TABLE Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 34/42] media: v4l2-compat-ioctl32: Fix timespec conversion Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 04/42] tcp: initialize rcv_mss to TCP_MIN_MSS instead of 0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 35/42] media: uvcvideo: Prevent heap overflow when accessing mapped controls Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 22:40 +0200
  [PATCH 3.18 24/42] scsi: sg: remove save_scat_len Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 14/42] block: Relax a check in blk_start_queue() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 18/42] scsi: zfcp: fix queuecommand for scsi_eh commands when DIX enabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 22/42] scsi: zfcp: trace HBA FSF response by default on dismiss or timedout late response Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 26/42] scsi: sg: off by one in sg_ioctl() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 23/42] scsi: zfcp: trace high part of "new" 64 bit SCSI LUN Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 02/42] qlge: avoid memcpy buffer overflow Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  [PATCH 3.18 13/42] powerpc: Fix DAR reporting when alignment handler faults Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-24 23:40 +0200
  Re: [PATCH 3.18 00/42] 3.18.72-stable review Guenter Roeck <linux@roeck-us.net> - 2017-09-25 03:10 +0200
    Re: [PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-25 08:40 +0200
      Re: [PATCH 3.18 00/42] 3.18.72-stable review Guenter Roeck <linux@roeck-us.net> - 2017-09-25 13:10 +0200
        Re: [PATCH 3.18 00/42] 3.18.72-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-09-25 14:30 +0200
  Re: [PATCH 3.18 00/42] 3.18.72-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2017-09-26 01:20 +0200

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