Re: [PATCH 06/16] x86/mm/ldt: Reserve high address-space range for the LDT

[Peter Zijlstra]

On Tue, Jan 16, 2018 at 02:51:45PM -0800, Andy Lutomirski wrote:
> On Tue, Jan 16, 2018 at 8:52 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > On Tue, Jan 16, 2018 at 05:36:49PM +0100, Joerg Roedel wrote:
> >> From: Joerg Roedel <jroedel@xxxxxxx>
> >>
> >> Reserve 2MB/4MB of address space for mapping the LDT to
> >> user-space.
> >
> > LDT is 64k, we need 2 per CPU, and NR_CPUS <= 64 on 32bit, that gives
> > 64K*2*64=8M > 2M.
> 
> If this works like it does on 64-bit, it only needs 128k regardless of
> the number of CPUs.  The LDT mapping is specific to the mm.

Ah, then I got my LDT things confused again... which is certainly
possible, we had a few too many variants back then.