linux-kernel - [tip:x86/urgent] x86/mm/pat: Disable preemption around __flush_tlb

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Date:   Mon, 29 Oct 2018 11:10:27 -0700
From:   tip-bot for Sebastian Andrzej Siewior <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
        peterz@...radead.org, tglx@...utronix.de, luto@...nel.org,
        bp@...en8.de, hpa@...or.com, bigeasy@...utronix.de,
        mingo@...nel.org
Subject: [tip:x86/urgent] x86/mm/pat: Disable preemption around
 __flush_tlb_all()

Commit-ID:  f77084d96355f5fba8e2c1fb3a51a393b1570de7
Gitweb:     https://git.kernel.org/tip/f77084d96355f5fba8e2c1fb3a51a393b1570de7
Author:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate: Wed, 17 Oct 2018 12:34:32 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Mon, 29 Oct 2018 19:04:31 +0100

x86/mm/pat: Disable preemption around __flush_tlb_all()

The WARN_ON_ONCE(__read_cr3() != build_cr3()) in switch_mm_irqs_off()
triggers every once in a while during a snapshotted system upgrade.

The warning triggers since commit decab0888e6e ("x86/mm: Remove
preempt_disable/enable() from __native_flush_tlb()"). The callchain is:

  get_page_from_freelist() -> post_alloc_hook() -> __kernel_map_pages()

with CONFIG_DEBUG_PAGEALLOC enabled.

Disable preemption during CR3 reset / __flush_tlb_all() and add a comment
why preemption has to be disabled so it won't be removed accidentaly.

Add another preemptible() check in __flush_tlb_all() to catch callers with
enabled preemption when PGE is enabled, because PGE enabled does not
trigger the warning in __native_flush_tlb(). Suggested by Andy Lutomirski.

Fixes: decab0888e6e ("x86/mm: Remove preempt_disable/enable() from __native_flush_tlb()")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20181017103432.zgv46nlu3hc7k4rq@linutronix.de
---
 arch/x86/include/asm/tlbflush.h | 6 ++++++
 arch/x86/mm/pageattr.c          | 6 +++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 323a313947e0..d760611cfc35 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -453,6 +453,12 @@ static inline void __native_flush_tlb_one_user(unsigned long addr)
  */
 static inline void __flush_tlb_all(void)
 {
+	/*
+	 * This is to catch users with enabled preemption and the PGE feature
+	 * and don't trigger the warning in __native_flush_tlb().
+	 */
+	VM_WARN_ON_ONCE(preemptible());
+
 	if (boot_cpu_has(X86_FEATURE_PGE)) {
 		__flush_tlb_global();
 	} else {
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 62bb30b4bd2a..a1004dec98ea 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -2309,9 +2309,13 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
 
 	/*
 	 * We should perform an IPI and flush all tlbs,
-	 * but that can deadlock->flush only current cpu:
+	 * but that can deadlock->flush only current cpu.
+	 * Preemption needs to be disabled around __flush_tlb_all() due to
+	 * CR3 reload in __native_flush_tlb().
 	 */
+	preempt_disable();
 	__flush_tlb_all();
+	preempt_enable();
 
 	arch_flush_lazy_mmu_mode();
 }