Question about pmap_kenter

Matthew Dillon dillon at
Tue May 25 14:08:35 PDT 2021

The documentation is out of date.

pmap_kenter() synchronizes the TLB on all CPUs.

pmap_kenter_quick() only invalidates the TLB on the current cpu.

pmap_kenter_noinval() does not touch the TLB at all.

The latter two functions are only used under controlled circumstances.
pmap_kenter_quick() is used when the caller only intends to use the mapping
on the current cpu, or intends to track which cpu's have synchronized the
mapping.   And pmap_kenter_noinval() is used when the caller is entering a
ton of PTEs into the pmap and will do a global invalidation when done.

pmap_qenter() passes an argument w/regard to what kind of tlb invalidation
is desired.

I should note that the buffer cache code (struct buf) tracks mapping
validity with a cpu mask, so operations on the buffer cache do not cause an
excessive number of global IPIs for SMP invalidations.

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