lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Tue, 1 Feb 2022 21:57:19 +0800 From: Wanpeng Li <kernellwp@...il.com> To: Paolo Bonzini <pbonzini@...hat.com> Cc: LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>, Sean Christopherson <seanjc@...gle.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>, Aili Yao <yaoaili@...gsoft.com> Subject: Re: [PATCH RESEND v2] KVM: LAPIC: Enable timer posted-interrupt when mwait/hlt is advertised On Tue, 1 Feb 2022 at 20:11, Paolo Bonzini <pbonzini@...hat.com> wrote: > > On 1/25/22 13:08, Wanpeng Li wrote: > > As commit 0c5f81dad46 (KVM: LAPIC: Inject timer interrupt via posted interrupt) > > mentioned that the host admin should well tune the guest setup, so that vCPUs > > are placed on isolated pCPUs, and with several pCPUs surplus for*busy* housekeeping. > > It is better to disable mwait/hlt/pause vmexits to keep the vCPUs in non-root > > mode. However, we may isolate pCPUs for other purpose like DPDK or we can make > > some guests isolated and others not, we may lose vmx preemption timer/timer fastpath > > due to not well tuned setup, and the checking in kvm_can_post_timer_interrupt() > > is not enough. Let's guarantee mwait/hlt is advertised before enabling posted-interrupt > > interrupt. vmx preemption timer/timer fastpath can continue to work if both of them > > are not advertised. > > Is this the same thing that you meant? > > -------- > As commit 0c5f81dad46 ("KVM: LAPIC: Inject timer interrupt via posted interrupt") > mentioned that the host admin should well tune the guest setup, so that vCPUs > are placed on isolated pCPUs, and with several pCPUs surplus for *busy* housekeeping. > In this setup, it is preferrable to disable mwait/hlt/pause vmexits to > keep the vCPUs in non-root mode. > > However, if only some guests isolated and others not, they would not have > any benefit from posted timer interrupts, and at the same time lose > VMX preemption timer fast paths because kvm_can_post_timer_interrupt() > returns true and therefore forces kvm_can_use_hv_timer() to false. > > By guaranteeing that posted-interrupt timer is only used if MWAIT or HLT > are done without vmexit, KVM can make a better choice and use the > VMX preemption timer and the corresponding fast paths. > -------- Looks better, thanks Paolo! :) Wanpeng
Powered by blists - more mailing lists