From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 3/5] KVM: add KVM_USER_EXIT vm ioctl for userspace exit Date: Wed, 5 Aug 2015 15:38:51 +0200 Message-ID: <55C211EB.2030704@redhat.com> References: <1438780877-31838-1-git-send-email-rkrcmar@redhat.com> <1438780877-31838-4-git-send-email-rkrcmar@redhat.com> <55C20FD2.8020607@redhat.com> <20150805133442.GA31952@potion.brq.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= Return-path: In-Reply-To: <20150805133442.GA31952@potion.brq.redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/08/2015 15:34, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > 2015-08-05 15:29+0200, Paolo Bonzini: >> On 05/08/2015 15:21, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: >>> + kvm_for_each_vcpu(idx, vcpu, kvm) >>> + if (vcpu->vcpu_id =3D=3D vcpu_id) { >>> + kvm_make_request(KVM_REQ_EXIT, vcpu); >>> + kvm_vcpu_kick(vcpu); >>> + >>> + return 0; >>> + } >>> + >> >> Why not a vcpu ioctl? kvm_for_each_vcpu can become pretty expensive= if >> you have a few dozen VCPUs. >=20 > Yeah, it will be slow, the only bright side is low frequency of calls= =2E >=20 > vcpu ioctl should only be issued by the vcpu thread so it would > significantly limit use. That's a general limitation, but you can lift it for particular ioctls. See in particular this: #if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS) /* * Special cases: vcpu ioctls that are asynchronous to vcpu exe= cution, * so vcpu_load() would break it. */ if (ioctl =3D=3D KVM_S390_INTERRUPT || ioctl =3D=3D KVM_S390_IR= Q || ioctl =3D=3D KVM_INTERRUPT) return kvm_arch_vcpu_ioctl(filp, ioctl, arg); #endif You can add an "if (ioctl =3D=3D KVM_USER_EXIT)" before. Paolo