[PATCH 1/8] x86/mm/pat: Disable preemption around __flush_tlb_all()

[Andrea Righi]

From: Sebastian Andrzej Siewior <bigeasy at linutronix.de>

BugLink: https://bugs.launchpad.net/bugs/1830433

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 at linutronix.de>
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Cc: Andy Lutomirski <luto at kernel.org>
Cc: Dave Hansen <dave.hansen at linux.intel.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Borislav Petkov <bp at alien8.de>
Cc: stable at vger.kernel.org
Link: https://lkml.kernel.org/r/20181017103432.zgv46nlu3hc7k4rq@linutronix.de
(cherry picked from commit f77084d96355f5fba8e2c1fb3a51a393b1570de7)
Tested-by: Connor Kuehl <connor.kuehl at canonical.com>
Signed-off-by: Andrea Righi <andrea.righi at canonical.com>
---
 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 1bbc43077583..1a56d1df5c21 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -473,6 +473,12 @@ 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 8d6c34fe49be..800de88208d7 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -2063,9 +2063,13 @@ 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();
 }
-- 
2.20.1