On Mon, Jun 17, 2019 at 11:07:45AM -0700, Dave Hansen wrote: > On 6/17/19 9:53 AM, Nadav Amit wrote: > >>> For anyone following along at home, I'm going to go off into crazy > >>> per-cpu-pgds speculation mode now... Feel free to stop reading now. :) > >>> > >>> But, I was thinking we could get away with not doing this on _every_ > >>> context switch at least. For instance, couldn't 'struct tlb_context' > >>> have PGD pointer (or two with PTI) in addition to the TLB info? That > >>> way we only do the copying when we change the context. Or does that tie > >>> the implementation up too much with PCIDs? > >> Hmm, that seems entirely reasonable. I think the nasty bit would be > >> figuring out all the interactions with PV TLB flushing. PV TLB > >> flushes already don't play so well with PCID tracking, and this will > >> make it worse. We probably need to rewrite all that code regardless. > > How is PCID (as you implemented) related to TLB flushing of kernel (not > > user) PTEs? These kernel PTEs would be global, so they would be invalidated > > from all the address-spaces using INVLPG, I presume. No? > > The idea is that you have a per-cpu address space. Certain kernel > virtual addresses would map to different physical address based on where > you are running. Each of the physical addresses would be "owned" by a > single CPU and would, by convention, never use a PGD that mapped an > address unless that CPU that "owned" it. > > In that case, you never really invalidate those addresses. But you would need to invalidate if the process moved to another CPU, correct?
