Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble memory as ROX

On Thu, Jun 01, 2023 at 06:13:44PM +0000, Edgecombe, Rick P wrote:

quoted

text_poke() _does_ create a separate RW mapping.

Sorry, I meant a separate RW allocation.

Ah yes, that makes sense

quoted

The thing that sucks about text_poke() is that it always does a full
TLB
flush, and AFAICT that's not remotely needed. What it really wants to
be
doing is conceptually just

kmap_local()
mempcy()
kunmap_loca()
flush_icache();

...except that kmap_local() won't actually create a new mapping on
non-highmem architectures, so text_poke() open codes it.

Text poke creates only a local CPU RW mapping. It's more secure because
other threads can't write to it.

*nod*, same as kmap_local

It also only needs to flush the local core when it's done since it's
not using a shared MM.

 
Ahh! Thanks for that; perhaps the comment in text_poke() about IPIs
could be a bit clearer.

What is it (if anything) you don't like about text_poke() then? It looks
like it's doing broadly similar things to kmap_local(), so should be
in the same ballpark from a performance POV?