> -----Original Message----- > From: Wei Wang [mailto:wei.w.wang@xxxxxxxxx] > Sent: Tuesday, September 18, 2018 5:58 PM > To: Andi Kleen <ak@xxxxxxxxxxxxxxx>; Gonglei (Arei) <arei.gonglei@xxxxxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; > kan.liang@xxxxxxxxx; peterz@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; > rkrcmar@xxxxxxxxxx; like.xu@xxxxxxxxx > Subject: Re: [PATCH v2 7/8] KVM: PMU: support to save/restore the guest lbr > stack on vCPU switching > > On 09/18/2018 10:56 AM, Andi Kleen wrote: > >>> From: Like Xu <like.xu@xxxxxxxxx> > >>> > >>> This patch adds support to KVM to save/restore the lbr stack on vCPU > >>> context switching. > >>> > >>> When the guest sets the ACTIVE bit of MSR_KVM_PV_LBR_CTRL, a perf > event > >>> is created on the host for the related vCPU. This perf event ensures the > >>> LBR stack to be saved/restored when the vCPU thread is scheduled out/in. > >>> The perf event is removed and freed when the guest clears the ACTIVE > >>> bit. > >>> > >> What about live migration? Does LBR stack need to be saved on the source > side and > >> restored on the dest side with the passthrough mode? > > Yes it should. Either for call stack LBR, or when it is frozen/disabled. > > > > When it's not frozen/disabled and not in call stack LBR mode it likely doesn't > > hurt either, but it's not strictly needed because it will > > be replaced so quickly. > > Yes, should be supported. We are working on v3 with the suggested lazy > save approach, and will send it out shortly. > Nice~ Thanks, -Gonglei
