[PATCH 5.9 291/391] powerpc/mce: Avoid nmi_enter/exit in real mode on pseries hash

[Greg Kroah-Hartman]

From: Ganesh Goudar <ganeshgr@xxxxxxxxxxxxx>

commit 8d0e2101274358d9b6b1f27232b40253ca48bab5 upstream.

Use of nmi_enter/exit in real mode handler causes the kernel to panic
and reboot on injecting SLB mutihit on pseries machine running in hash
MMU mode, because these calls try to accesses memory outside RMO
region in real mode handler where translation is disabled.

Add check to not to use these calls on pseries machine running in hash
MMU mode.

Fixes: 116ac378bb3f ("powerpc/64s: machine check interrupt update NMI accounting")
Cc: stable@xxxxxxxxxxxxxxx # v5.8+
Signed-off-by: Ganesh Goudar <ganeshgr@xxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20201009064005.19777-2-ganeshgr@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/powerpc/kernel/mce.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/arch/powerpc/kernel/mce.c
+++ b/arch/powerpc/kernel/mce.c
@@ -591,12 +591,11 @@ EXPORT_SYMBOL_GPL(machine_check_print_ev
 long notrace machine_check_early(struct pt_regs *regs)
 {
 	long handled = 0;
-	bool nested = in_nmi();
 	u8 ftrace_enabled = this_cpu_get_ftrace_enabled();
 
 	this_cpu_set_ftrace_enabled(0);
-
-	if (!nested)
+	/* Do not use nmi_enter/exit for pseries hpte guest */
+	if (radix_enabled() || !firmware_has_feature(FW_FEATURE_LPAR))
 		nmi_enter();
 
 	hv_nmi_check_nonrecoverable(regs);
@@ -607,7 +606,7 @@ long notrace machine_check_early(struct
 	if (ppc_md.machine_check_early)
 		handled = ppc_md.machine_check_early(regs);
 
-	if (!nested)
+	if (radix_enabled() || !firmware_has_feature(FW_FEATURE_LPAR))
 		nmi_exit();
 
 	this_cpu_set_ftrace_enabled(ftrace_enabled);