linux-kernel - Re: [PATCH v2 1/7] modules: Create rlimit for module space

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Date:   Sat, 13 Oct 2018 00:04:14 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "jannh@...gle.com" <jannh@...gle.com>
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Subject: Re: [PATCH v2 1/7] modules: Create rlimit for module space

On Fri, 2018-10-12 at 19:22 +0200, Jann Horn wrote:
> On Fri, Oct 12, 2018 at 7:04 PM Edgecombe, Rick P
> <rick.p.edgecombe@...el.com> wrote:
> > On Fri, 2018-10-12 at 02:35 +0200, Jann Horn wrote:
> > > Why all the rbtree stuff instead of stashing a pointer in struct
> > > vmap_area, or something like that?
> > 
> > Since the tracking was not for all vmalloc usage, the intention was to not
> > bloat
> > the structure for other usages likes stacks. I thought usually there
> > wouldn't be
> > nearly as much module space allocations as there would be kernel stacks, but
> > I
> > didn't do any actual measurements on the tradeoffs.
> 
> I imagine that one extra pointer in there - pointing to your struct
> mod_alloc_user - would probably not be terrible. 8 bytes more per
> kernel stack shouldn't be so bad?

I looked into this and it starts to look a little messy. The nommu.c version of
vmalloc doesn't use or expose access to vmap_area or vm_struct. So it starts to
look like a bunch of IFDEFs to remove the rlimit in the nommu case or making a
stand in that maintains pretend vm struct's in nommu.c. I had actually
previously tried to at least pull the allocations size from vmalloc structs, but it broke on nommu.

Thought I would check back and see. How important do you think this is?