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

Sebastian Andrzej Siewior · KAGA-KOKO · commit f77084d96355 · 2018-10-29T19:04:31.000+01:00
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 decab08 ("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: decab08 ("x86/mm: Remove preempt_disable/enable() from __native_flush_tlb()") Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Borislav Petkov <bp@alien8.de> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20181017103432.zgv46nlu3hc7k4rq@linutronix.de
diff --git 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
@@ -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();
 }
