[PATCH 1/3] x86/mm/pat: Disable preemption around __flush_tlb_all()

[Sebastian Andrzej Siewior]

I've seen the WARN_ON_ONCE(__read_cr3() != build_cr3()) in
switch_mm_irqs_off() every once in a while during a snapshotted system
upgrade.
I also saw the warning early during which was introduced in 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.

Turns out, once I disable preemption around __flush_tlb_all() both
warnings do not appear.

Disable preemption during CR3 reset / __flush_tlb_all().

Fixes: decab0888e6e ("x86/mm: Remove preempt_disable/enable() from __native_flush_tlb()")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 arch/x86/mm/pageattr.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 51a5a69ecac9f..fe6b21f0a6631 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -2088,7 +2088,9 @@ 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:
 	 */
+	preempt_disable();
 	__flush_tlb_all();
+	preempt_enable();
 
 	arch_flush_lazy_mmu_mode();
 }
-- 
2.19.1