The lazy MMU mode cannot be used in interrupt context. This is
documented in <linux/pgtable.h>, but isn't consistently handled
across architectures.

arm64 ensures that calls to lazy_mmu_mode_* have no effect in
interrupt context, because such calls do occur in certain
configurations - see commit b81c688426a9 ("arm64/mm: Disable barrier
batching in interrupt contexts"). Other architectures do not check
this situation, most likely because it hasn't occurred so far.

Both arm64 and x86/Xen also ensure that any lazy MMU optimisation is
disabled while in interrupt mode (see queue_pte_barriers() and
xen_get_lazy_mode() respectively).

Let's handle this in the new generic lazy_mmu layer, in the same
fashion as arm64: bail out of lazy_mmu_mode_* if in_interrupt(), and
have in_lazy_mmu_mode() return false to disable any optimisation.
Also remove the arm64 handling that is now redundant; x86/Xen has
its own internal tracking so it is left unchanged.

Signed-off-by: Kevin Brodsky <redacted>
---
  arch/arm64/include/asm/pgtable.h | 17 +----------------
  include/linux/pgtable.h          | 16 ++++++++++++++--
  include/linux/sched.h            |  3 +++
  3 files changed, 18 insertions(+), 18 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 944e512767db..a37f417c30be 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h

@@ -62,37 +62,22 @@ static inline void emit_pte_barriers(void)
  
  static inline void queue_pte_barriers(void)
  {
-	if (in_interrupt()) {
-		emit_pte_barriers();
-		return;
-	}
-