[PATCH 3.16 125/328] powerpc/pseries: Fix endianness while restoring of r3 in MCE handler.

From: Ben Hutchings
Date: Sun Dec 09 2018 - 17:12:57 EST

3.16.62-rc1 review patch. If anyone has any objections, please let me know.


From: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>

commit cd813e1cd7122f2c261dce5b54d1e0c97f80e1a5 upstream.

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.

Severe Machine check interrupt [Recovered]
NIP [d00000000ca301b8]: init_module+0x1b8/0x338 [bork_kernel]
Initiator: CPU
Error type: SLB [Multihit]
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
init_module+0x1c0/0x338 [bork_kernel]
--- Exception: c00 (System Call) at 00007fff8bda0644
SP (7fffdfbfe980) is in userspace

This patch fixes this issue.

Fixes: a08a53ea4c97 ("powerpc/le: Enable RTAS events support")
Reviewed-by: Nicholas Piggin <npiggin@xxxxxxxxx>
Signed-off-by: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
arch/powerpc/platforms/pseries/ras.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/platforms/pseries/ras.c
+++ b/arch/powerpc/platforms/pseries/ras.c
@@ -298,7 +298,7 @@ static struct rtas_error_log *fwnmi_get_

savep = __va(regs->gpr[3]);
- regs->gpr[3] = savep[0]; /* restore original r3 */
+ regs->gpr[3] = be64_to_cpu(savep[0]); /* restore original r3 */

/* If it isn't an extended log we can use the per cpu 64bit buffer */
h = (struct rtas_error_log *)&savep[1];