On 01/07/2018 04:05 AM, Thomas Gleixner wrote: >> static DEFINE_SPINLOCK(shadow_table_allocation_lock); >> >> Now I have my suspicions why that's not needed anymore upstream but I'd >> let tglx explain better. > We got rid of all that runtime mapping stuff and the functions are only > called from pti_init(). So the locking and therefor the tests above are not > needed anymore. While at it we should mark all those function __init. Yes, the double-test was part of an optimization where we attempted to avoid using a global spinlock in the fork() path. We would check for unallocated mid-level page tables without the lock. The lock was only taken it when we needed to *make* an entry to avoid collisions. Now that it is all single-threaded, there is no chance of a collision, no need for a lock, and no need for the re-check. ^^ Just in case someone wants to include a bit more first-hand information about wtf that code was doing there.