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+/**
+ * arch_update_kernel_mappings_end - A batch of kernel pgtable mappings have
+ * been updated.
+ * @start: Virtual address of start of range that was updated.
+ * @end: Virtual address of end of range that was updated.
+ *
+ * An optional hook to inform architecture code that a batch update is complete.
+ * This balances a previous call to arch_update_kernel_mappings_begin().
+ *
+ * An architecture may override this for any purpose, such as exiting a lazy
+ * mode previously entered with arch_update_kernel_mappings_begin() or syncing
+ * kernel mappings to a secondary pgtable. The default implementation calls an
+ * arch-provided arch_sync_kernel_mappings() if any arch-defined pgtable level
+ * was updated.
+ *
+ * Context: Called in task context and may be preemptible.
+ */
+static inline void arch_update_kernel_mappings_end(unsigned long start,
+						   unsigned long end,
+						   pgtbl_mod_mask mask)
+{
+	if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
+		arch_sync_kernel_mappings(start, end);
+}

One arch call back calling yet another arch call back sounds bit odd. 

It's no different from the default implementation of arch_make_huge_pte()
calling pte_mkhuge() is it?

Agreed. arch_make_huge_pte() ---> pte_mkhuge() where either helpers can be
customized in the platform is another such example but unless necessary we
should probably avoid following that. Anyways it's not a big deal I guess.

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Also
should not ARCH_PAGE_TABLE_SYNC_MASK be checked both for __begin and __end
callbacks in case a platform subscribes into this framework. 

I'm not sure how that would work? The mask is accumulated during the pgtable
walk. So we don't have a mask until we get to the end.

A non-zero ARCH_PAGE_TABLE_SYNC_MASK indicates that a platform is subscribing
to this mechanism. So could ARCH_PAGE_TABLE_SYNC_MASK != 0 be used instead ?

There are now 2 levels of mechanism:

Either: arch defines ARCH_PAGE_TABLE_SYNC_MASK to be non-zero and provides
arch_sync_kernel_mappings(). This is unchanged from how it was before.

Or: arch defines it's own version of one or both of
arch_update_kernel_mappings_begin() and arch_update_kernel_mappings_end().

So a non-zero ARCH_PAGE_TABLE_SYNC_MASK indicates that a platform is subscribing
to the *first* mechanism. It has nothing to do with the second mechanism. If the
platform defines arch_update_kernel_mappings_begin() it wants it to be called.
If it doesn't define it, then it doesn't get called.

Thanks,
Ryan