Dave Hansen wrote: > On Thu, 2008-03-20 at 21:35 +0100, Carsten Otte wrote: >> Dave Hansen wrote: >>> Well, and more fundamentally: do we really want dup_mm() able to be >>> called from other code? >>> >>> Maybe we need a bit more detailed justification why fork() itself isn't >>> good enough. It looks to me like they basically need an arch-specific >>> argument to fork, telling the new process's page tables to take the >>> fancy new bit. >>> >>> I'm really curious how this new stuff is going to get used. Are you >>> basically replacing fork() when creating kvm guests? >> No. The trick is, that we do need bigger page tables when running >> guests: our page tables are usually 2k, but when running a guest >> they're 4k to track both guest and host dirty&reference information. >> This looks like this: >> *----------* >> *2k PTE's * >> *----------* >> *2k PGSTE * >> *----------* >> We don't want to waste precious memory for all page tables. We'd like >> to have one kernel image that runs regular server workload _and_ >> guests. > > That makes a lot of sense. > > Is that layout (the shadow and regular stacked together) specified in > hardware somehow, or was it just chosen? It's defined by hardware. The chip just adds +2k to the ptep to get to the corresponding pgste. Both pte and pgste are 64bit per page. I know Heiko and Martin have thought a lot about possible races. I'll have to leave your question on the race against pfault open for them. Btw: thanks a lot for reviewing our changes :-) cheers, Carsten _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
