I don't see why the kernel can't map this magic page to the same
virtual address for each process. I assumed you'd want to do that for
code anyway.
> > 1b) user-space can look for the known page and read values from it, if
> > it wants
>
> It's not about reading values. The time offsets are completely
> useless if the CPU doesn't support rdtsc. We want to export CODE,
> not data.
Yeah, OK. But user-space can MAP_INHERIT the code which is appropriate
for the CPU.
> > 2) MAP_INHERIT can be used by user-space to implement
> > machine-specific code.
>
> Sure. MAP_INHERIT can be used for general-purpose things. But
> MAP_INHERIT is not going to happen. It has security issues that you
> ignore,a dn it has performance issues for process creation (we can't
> just completely break down and re-build the page tables, we have to
> be careful). End of story.
Why do you say I've ignored the security issues? I've suggested a
number of ways of dealing with that. I've not seen any replies saying
that the solutions are flawed.
The re-building page table argument sounds like it's the killer,
though. I assume you're saying that we'd lose VM optimisations if we
have to avoid touching certain vma's when tearing down page tables?
Regards,
Richard....
Permanent: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca
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