From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Tue, 11 Dec 2018 21:53:43 +0100
Subject: x86/mm/pat: disable preemption __split_large_page() after spin_lock()
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 3f75a77fadb2cd11af3b76a52581a9e139ded210
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

[ Upstream commit 45c6ff4811878e5c1c2ae31303cd95cdc6ae2ab4 ]

Commit "x86/mm/pat: Disable preemption around __flush_tlb_all()" added a
warning if __flush_tlb_all() is invoked in preemptible context. On !RT
the warning does not trigger because a spin lock is acquired which
disables preemption. On RT the spin lock does not disable preemption and
so the warning is seen.

Disable preemption to avoid the warning __flush_tlb_all().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 arch/x86/mm/pageattr.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -662,11 +662,17 @@ __split_large_page(struct cpa_data *cpa,
 
 	spin_lock(&pgd_lock);
 	/*
+	 * Keep preemption disabled after __flush_tlb_all() which expects not be
+	 * preempted during the flush of the local TLB.
+	 */
+	preempt_disable();
+	/*
 	 * Check for races, another CPU might have split this page
 	 * up for us already:
 	 */
 	tmp = _lookup_address_cpa(cpa, address, &level);
 	if (tmp != kpte) {
+		preempt_enable();
 		spin_unlock(&pgd_lock);
 		return 1;
 	}
@@ -696,6 +702,7 @@ __split_large_page(struct cpa_data *cpa,
 		break;
 
 	default:
+		preempt_enable();
 		spin_unlock(&pgd_lock);
 		return 1;
 	}
@@ -743,6 +750,7 @@ __split_large_page(struct cpa_data *cpa,
 	 * going on.
 	 */
 	__flush_tlb_all();
+	preempt_enable();
 	spin_unlock(&pgd_lock);
 
 	return 0;