=- > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Liu Yu > Sent: Tuesday, July 29, 2008 3:48 PM > To: Christian Ehrhardt > Cc: Hollis Blanchard; [EMAIL PROTECTED]; > [EMAIL PROTECTED]; [email protected] > Subject: RE: [PATCH 5 of 5] kvm: powerpc: Map guest userspace > with TID=0 mappings > > > > -----Original Message----- > > From: Christian Ehrhardt [mailto:[EMAIL PROTECTED] > > Sent: Tuesday, July 29, 2008 3:03 PM > > To: Liu Yu > > Cc: Hollis Blanchard; [EMAIL PROTECTED]; [EMAIL PROTECTED]; > > [email protected] > > 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?
I see. 'kvm_arch_vcpu_load' and 'kvm_arch_vcpu_put' will handle this in preempt hooker. > > > > > > 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 > [EMAIL PROTECTED] More majordomo info at > http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
