[RFC PATCH v2 00/15] pkeys-based page table hardening

[Dave Hansen]

One of the sticker things in the x86 attempt to do the same thing was
context switching, both between normal tasks and in/out of exceptions
and interrupts.

The easiest place this manifested for us was code chunk like this:

	kpkeys_set_level(KPKEYS_LVL_PGTABLES);
	// modify page tables here
	kpkeys_restore_pkey_reg();

We had to make sure that we didn't get preempted and context switch over
to some other task that _wasn't_ doing page table manipulation while
page table writes were allowed.

On x86, we had to basically start context-switching the kernel pkey
register the same way we do GPRs.

How is SYS_POR_EL0 being context switched?