modules: Use vmalloc special flag

Use new flag for handling freeing of special permissioned memory in vmalloc
and remove places where memory was set RW before freeing which is no longer
needed.

Since freeing of VM_FLUSH_RESET_PERMS memory is not supported in an
interrupt by vmalloc, the freeing of init sections is moved to a work
queue. Instead of call_rcu it now uses synchronize_rcu() in the work
queue.

Lastly, there is now a WARN_ON in module_memfree since it should not be
called in an interrupt with special memory as is required for
VM_FLUSH_RESET_PERMS.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <akpm@linux-foundation.org>
Cc: <ard.biesheuvel@linaro.org>
Cc: <deneen.t.dock@intel.com>
Cc: <kernel-hardening@lists.openwall.com>
Cc: <kristen@linux.intel.com>
Cc: <linux_dti@icloud.com>
Cc: <will.deacon@arm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190426001143.4983-18-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>