KVM: LAPIC: Enable timer posted-interrupt only when mwait/hlt is advertised
authorWanpeng Li <wanpengli@tencent.com>
Tue, 25 Jan 2022 12:08:58 +0000 (04:08 -0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 12 May 2022 10:30:25 +0000 (12:30 +0200)
commit680e982ae89b64c0b8b1a81d8d9031e4ab01bc0f
tree03e9add128e706594d2aef1404be02d508d6efd6
parent8e10a00b18769a757af763d4f55c4204200f44ef
KVM: LAPIC: Enable timer posted-interrupt only when mwait/hlt is advertised

[ Upstream commit 1714a4eb6fb0cb79f182873cd011a8ed60ac65e8 ]

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.

Reported-by: Aili Yao <yaoaili@kingsoft.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Cc: Aili Yao <yaoaili@kingsoft.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1643112538-36743-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
arch/x86/kvm/lapic.c