Messages in this thread | | | Date | Mon, 18 Dec 2017 21:57:32 +0100 | From | Peter Zijlstra <> | Subject | Re: [patch V163 27/51] x86/mm/pti: Populate user PGD |
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On Mon, Dec 18, 2017 at 12:45:13PM -0800, Dave Hansen wrote: > On 12/18/2017 12:41 PM, Peter Zijlstra wrote: > >> I also don't think the user_shared area of the fixmap can get *that* > >> big. Does anybody know offhand what the theoretical limits are there? > > Problem there is the nr_cpus term I think, we currently have up to 8k > > CPUs, but I can see that getting bigger in the future. > > It only matters if we go over 512GB, though. Is the per-cpu part of the > fixmap ever more than 512GB/8k=64MB?
Unlikely, I think the LDT (@ 32 pages / 128K) and the DS (@ 2*4 pages / 32K) are the largest entries in there.
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