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

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Message-ID: <ZH0GeKreazeNYmHT@moria.home.lan>
Date:   Sun, 4 Jun 2023 17:47:36 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH 12/13] x86/jitalloc: prepare to allocate exectuatble
 memory as ROX

On Thu, Jun 01, 2023 at 08:50:39PM +0000, Edgecombe, Rick P wrote:
> > 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?
> 
> The way text_poke() is used here, it is creating a new writable alias
> and flushing it for *each* write to the module (like for each write of
> an individual relocation, etc). I was just thinking it might warrant
> some batching or something.

Ah, I see. A kmap_local type interface might get us that kind of
batching, if it supported mapping compound pages - currently kmap_local
still only maps single pages, but with folios getting plumbed around I
assume someone will make it handle compound pages eventually.