Re: [patch 02/02] Debug option to write-protect rodata: the write protect logic and config option

[Coywolf Qi Hunt <coywolf@gmail.com>]

2005/11/7, Arjan van de Ven <arjan@infradead.org>:
> On Mon, 2005-11-07 at 08:06 -0600, Josh Boyer wrote:
> > On Mon, 2005-11-07 at 10:58 +0000, arjan@infradead.org wrote:
> > > Hi,
> > >
> > > I've been working on a patch that turns the kernel's .rodata section to be
> > > actually read only, eg any write attempts to it cause a segmentation fault.
> > >
> > > This patch introduces the actual debug option to catch any writes to rodata
> >
> > Why a debug option?  From what I can tell, it doesn't impact runtime
> > performance much and it provides good protection.  Any reason not to
> > make it an always-on feature?
>
> personally I'd like that but there is a chance of a tiny perf regression
> and usually there are people objecting to that.
>
> (It's not clear cut: while the last bit of the kernel no longer is
> covered by a 2Mb tlb, most intel cpus have very few of such tlbs in the
> first place and this would free up one such tlb for other things (say
> the stack data) or even the userspace database), so it's not all that
> clear cut what the cost of this is)

I'm dumb. But how is "the last bit of the kernel no longer is covered
by a 2Mb tlb"? Could you explain a bit more?
--
Coywolf Qi Hunt
http://sosdg.org/~coywolf/