linux-kernel - [PATCH] x86/mm/pat: Fix missing preemption disable for __native_flush

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Date:   Fri, 09 Nov 2018 16:05:47 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     tglx@...utronix.de
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, stable@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] x86/mm/pat: Fix missing preemption disable for
 __native_flush_tlb()

Commit f77084d96355 "x86/mm/pat: Disable preemption around
__flush_tlb_all()" addressed a case where __flush_tlb_all() is called
without preemption being disabled. It also left a warning to catch other
cases where preemption is not disabled. That warning triggers for the
memory hotplug path which is also used for persistent memory enabling:

 WARNING: CPU: 35 PID: 911 at ./arch/x86/include/asm/tlbflush.h:460
 RIP: 0010:__flush_tlb_all+0x1b/0x3a
 [..]
 Call Trace:
  phys_pud_init+0x29c/0x2bb
  kernel_physical_mapping_init+0xfc/0x219
  init_memory_mapping+0x1a5/0x3b0
  arch_add_memory+0x2c/0x50
  devm_memremap_pages+0x3aa/0x610
  pmem_attach_disk+0x585/0x700 [nd_pmem]

Rather than audit all __flush_tlb_all() callers to add preemption, just
do it internally to __flush_tlb_all().

Fixes: f77084d96355 ("x86/mm/pat: Disable preemption around __flush_tlb_all()")
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: 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>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 arch/x86/include/asm/tlbflush.h |    8 ++++----
 arch/x86/mm/pageattr.c          |    6 +-----
 2 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index d760611cfc35..049e0aca0fb5 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -454,11 +454,10 @@ 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().
+	 *  Preemption needs to be disabled around __flush_tlb* calls
+	 *  due to CR3 reload in __native_flush_tlb().
 	 */
-	VM_WARN_ON_ONCE(preemptible());
-
+	preempt_disable();
 	if (boot_cpu_has(X86_FEATURE_PGE)) {
 		__flush_tlb_global();
 	} else {
@@ -467,6 +466,7 @@ static inline void __flush_tlb_all(void)
 		 */
 		__flush_tlb();
 	}
+	preempt_enable();
 }
 
 /*
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index db7a10082238..f799076e3d57 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -2309,13 +2309,9 @@ 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.
-	 * Preemption needs to be disabled around __flush_tlb_all() due to
-	 * CR3 reload in __native_flush_tlb().
+	 * but that can deadlock->flush only current cpu:
 	 */
-	preempt_disable();
 	__flush_tlb_all();
-	preempt_enable();
 
 	arch_flush_lazy_mmu_mode();
 }