sparc/mm: disable preemption in lazy mmu mode

Since commit 38e0edb15bd0 ("mm/apply_to_range: call pte function with lazy
updates") it's been possible for arch_[enter|leave]_lazy_mmu_mode() to be
called without holding a page table lock (for the kernel mappings case),
and therefore it is possible that preemption may occur while in the lazy
mmu mode. The Sparc lazy mmu implementation is not robust to preemption
since it stores the lazy mode state in a per-cpu structure and does not
attempt to manage that state on task switch.

Powerpc had the same issue and fixed it by explicitly disabling preemption
in arch_enter_lazy_mmu_mode() and re-enabling in
arch_leave_lazy_mmu_mode(). See commit b9ef323ea168 ("powerpc/64s:
Disable preemption in hash lazy mmu mode").

Given Sparc's lazy mmu mode is based on powerpc's, let's fix it in the
same way here.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 38e0edb15bd0 ("mm/apply_to_range: call pte function with lazy updates")
Signed-off-by: Ryan Roberts <[e-mail]>
Acked-by: David Hildenbrand <[e-mail]>
Acked-by: Andreas Larsson <[e-mail]>
Acked-by: Juergen Gross <[e-mail]>
Cc: Borislav Betkov <[e-mail]>
Cc: Boris Ostrovsky <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Juegren Gross <[e-mail]>
Cc: Matthew Wilcow (Oracle) <[e-mail]>
Cc: Thomas Gleinxer <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/sparc/mm/tlb.c

···
 
 void arch_enter_lazy_mmu_mode(void)
 {
-	struct tlb_batch *tb = this_cpu_ptr(&tlb_batch);
+	struct tlb_batch *tb;
 
+	preempt_disable();
+	tb = this_cpu_ptr(&tlb_batch);
 	tb->active = 1;
 }
 
···
 	if (tb->tlb_nr)
 		flush_tlb_pending();
 	tb->active = 0;
+	preempt_enable();
 }
 
 static void tlb_batch_add_one(struct mm_struct *mm, unsigned long vaddr,