[PATCH v4 2/6] powerpc/pseries: Fix endainness while restoring of r3 in MCE handler.

[Mahesh J Salgaonkar]

From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>

During Machine Check interrupt on pseries platform, register r3 points
RTAS extended event log passed by hypervisor. Since hypervisor uses r3
to pass pointer to rtas log, it stores the original r3 value at the
start of the memory (first 8 bytes) pointed by r3. Since hypervisor
stores this info and rtas log is in BE format, linux should make
sure to restore r3 value in correct endian format.

Without this patch when MCE handler, after recovery, returns to code that
that caused the MCE may end up with Data SLB access interrupt for invalid
address followed by kernel panic or hang.

[   62.878965] Severe Machine check interrupt [Recovered]
[   62.878968]   NIP [d00000000ca301b8]: init_module+0x1b8/0x338 [bork_kernel]
[   62.878969]   Initiator: CPU
[   62.878970]   Error type: SLB [Multihit]
[   62.878971]     Effective address: d00000000ca70000
cpu 0xa: Vector: 380 (Data SLB Access) at [c0000000fc7775b0]
    pc: c0000000009694c0: vsnprintf+0x80/0x480
    lr: c0000000009698e0: vscnprintf+0x20/0x60
    sp: c0000000fc777830
   msr: 8000000002009033
   dar: a803a30c000000d0
  current = 0xc00000000bc9ef00
  paca    = 0xc00000001eca5c00	 softe: 3	 irq_happened: 0x01
    pid   = 8860, comm = insmod
[c0000000fc7778b0] c0000000009698e0 vscnprintf+0x20/0x60
[c0000000fc7778e0] c00000000016b6c4 vprintk_emit+0xb4/0x4b0
[c0000000fc777960] c00000000016d40c vprintk_func+0x5c/0xd0
[c0000000fc777980] c00000000016cbb4 printk+0x38/0x4c
[c0000000fc7779a0] d00000000ca301c0 init_module+0x1c0/0x338 [bork_kernel]
[c0000000fc777a40] c00000000000d9c4 do_one_initcall+0x54/0x230
[c0000000fc777b00] c0000000001b3b74 do_init_module+0x8c/0x248
[c0000000fc777b90] c0000000001b2478 load_module+0x12b8/0x15b0
[c0000000fc777d30] c0000000001b29e8 sys_finit_module+0xa8/0x110
[c0000000fc777e30] c00000000000b204 system_call+0x58/0x6c
--- Exception: c00 (System Call) at 00007fff8bda0644
SP (7fffdfbfe980) is in userspace

This patch fixes this issue.

Fixes: a08a53ea4c97 ("powerpc/le: Enable RTAS events support")
Cc: stable at vger.kernel.org
Reviewed-by: Nicholas Piggin <npiggin at gmail.com>
Signed-off-by: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
---
 arch/powerpc/platforms/pseries/ras.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
index f6ba9a2a4f84..e3bd849141de 100644
--- a/arch/powerpc/platforms/pseries/ras.c
+++ b/arch/powerpc/platforms/pseries/ras.c
@@ -362,7 +362,7 @@ static struct rtas_error_log *fwnmi_get_errinfo(struct pt_regs *regs)
 	}
 
 	savep = __va(regs->gpr[3]);
-	regs->gpr[3] = savep[0];	/* restore original r3 */
+	regs->gpr[3] = be64_to_cpu(savep[0]);	/* restore original r3 */
 
 	h = (struct rtas_error_log *)&savep[1];
 	/* Use the per cpu buffer from paca to store rtas error log */