> -----Original Message----- > From: Christian Ehrhardt [mailto:ehrhardt@xxxxxxxxxxxxxxxxxx] > Sent: Tuesday, July 29, 2008 3:03 PM > To: Liu Yu > Cc: Hollis Blanchard; avi@xxxxxxxxxxxx; > kvm-ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 5 of 5] kvm: powerpc: Map guest userspace > with TID=0 mappings > > On Monday 28 July 2008 12:33:41 Liu Yu wrote: > > I have a question that I could not think through. > > While multiple qemu/kvm processes are running at the same > time, how to > > prevent one guest from using others' TLB? For all the > guests have the > > same TID=0 for userspace and TID=1 for kernel. > [...] > > Hi Yu Liu, thats a good question. > Afaik thats solved by the fact that the shadow tlb which is > used when entering guest context is per vcpu. Therefor a > guest has always it's own shadow tlb active and no mappings > to the content of other guests. Yes, shadow tlb is per vcpu. But in the patch 4/5, before entering guest context, not all shadow tlb will be written back. So if (guest A -> guest B) happen, after entering guest B, is there any possibility that A's tlb is still existing in hardware? > > This patch just allows us that a single guest userspace > process accessing the kernel 20 times (and changing privilege > level 20 times by doing so) can run without tlb flushes. > Guest-userspace context switch (pid is changing) -> tlb > flush; and guest switches (guest A -> guest B) -> other > shadow tlb active; should still be working fine. > > > > > > > The net is that we don't need to flush the TLB on privilege > > > switches, but we do on guest context switches (which are far > > > more infrequent). Guest boot time performance > improvement: about 30%. > > > > > -- > > Grüsse / regards, > Christian Ehrhardt > IBM Linux Technology Center, Open Virtualization > -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
