From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Mon, 12 Mar 2018 15:29:19 +0000 (-0400)
Subject: x86/spectre_v2: Fix cpu offlining with IPBP.
X-Git-Tag: v4.1.12-124.31.3~914
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=b5b92b810c765ccaa300c5fb3b6ab6ce4cf0464d;p=users%2Fjedix%2Flinux-maple.git

x86/spectre_v2: Fix cpu offlining with IPBP.

We didn't check if tsk->mm is available when an CPU goes down - and
of course - that is exactly when there is no task.

As such we would crash.

OraBug: 27678629
Reveiwed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Jack Vogel <jack.vogel@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 4d6ed0734975..620d4af6a784 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -107,7 +107,7 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
 	if (likely(prev != next)) {
 
 		/* Null tsk means switching to kernel, so that's safe */
-		if (ibpb_inuse && tsk &&
+		if (ibpb_inuse && tsk && tsk->mm &&
 		   get_dumpable(tsk->mm) != SUID_DUMP_USER)
 			native_wrmsrl(MSR_IA32_PRED_CMD, FEATURE_SET_IBPB);