From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v4 07/10] limit number of VCPUs on demand Date: Tue, 30 Jun 2015 17:09:53 +0100 Message-ID: <20150630160949.GR27725@arm.com> References: <1435324578-21832-1-git-send-email-andre.przywara@arm.com> <1435324578-21832-8-git-send-email-andre.przywara@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id F1E8556B32 for ; Tue, 30 Jun 2015 11:58:45 -0400 (EDT) Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Ei0NFcP2jVFN for ; Tue, 30 Jun 2015 11:58:44 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by mm01.cs.columbia.edu (Postfix) with ESMTP id A622F54493 for ; Tue, 30 Jun 2015 11:58:44 -0400 (EDT) Content-Disposition: inline In-Reply-To: <1435324578-21832-8-git-send-email-andre.przywara@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu To: Andre Przywara Cc: Marc Zyngier , "penberg@kernel.org" , "kvmarm@lists.cs.columbia.edu" , "kvm@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" List-Id: kvmarm@lists.cs.columbia.edu On Fri, Jun 26, 2015 at 02:16:15PM +0100, Andre Przywara wrote: > Currently the ARM GIC checks the number of VCPUs against a fixed > limit, which is GICv2 specific. Don't pretend we know better than the > kernel and let's get rid of that explicit check. > Instead be more relaxed about KVM_CREATE_VCPU failing with EINVAL, > which is the way the kernel communicates having reached a VCPU limit. > If we see this and have at least brought up one VCPU already > successfully, then don't panic, but limit the number of VCPUs instead. > > Signed-off-by: Andre Przywara > --- > arm/gic.c | 6 ------ > arm/kvm-cpu.c | 7 ++++++- > kvm-cpu.c | 7 +++++++ > 3 files changed, 13 insertions(+), 7 deletions(-) > > diff --git a/arm/gic.c b/arm/gic.c > index 99f0d2b..05f85a2 100644 > --- a/arm/gic.c > +++ b/arm/gic.c > @@ -84,12 +84,6 @@ int gic__create(struct kvm *kvm) > { > int err; > > - if (kvm->nrcpus > GIC_MAX_CPUS) { > - pr_warning("%d CPUS greater than maximum of %d -- truncating\n", > - kvm->nrcpus, GIC_MAX_CPUS); > - kvm->nrcpus = GIC_MAX_CPUS; > - } > - > /* Try the new way first, and fallback on legacy method otherwise */ > err = gic__create_device(kvm); > if (err) > diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c > index 7780251..b2fd6ed 100644 > --- a/arm/kvm-cpu.c > +++ b/arm/kvm-cpu.c > @@ -51,8 +51,13 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id) > return NULL; > > vcpu->vcpu_fd = ioctl(kvm->vm_fd, KVM_CREATE_VCPU, cpu_id); > - if (vcpu->vcpu_fd < 0) > + if (vcpu->vcpu_fd < 0) { > + if (errno == EINVAL) { > + free(vcpu); > + return NULL; > + } Hmm, but EINVAL can mean all sorts of other failures too, surely? I'm not against removing the nrcpus check, but I think we should die if ioctls start failing rather than silently ignore them. Will From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Tue, 30 Jun 2015 17:09:53 +0100 Subject: [PATCH v4 07/10] limit number of VCPUs on demand In-Reply-To: <1435324578-21832-8-git-send-email-andre.przywara@arm.com> References: <1435324578-21832-1-git-send-email-andre.przywara@arm.com> <1435324578-21832-8-git-send-email-andre.przywara@arm.com> Message-ID: <20150630160949.GR27725@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Fri, Jun 26, 2015 at 02:16:15PM +0100, Andre Przywara wrote: > Currently the ARM GIC checks the number of VCPUs against a fixed > limit, which is GICv2 specific. Don't pretend we know better than the > kernel and let's get rid of that explicit check. > Instead be more relaxed about KVM_CREATE_VCPU failing with EINVAL, > which is the way the kernel communicates having reached a VCPU limit. > If we see this and have at least brought up one VCPU already > successfully, then don't panic, but limit the number of VCPUs instead. > > Signed-off-by: Andre Przywara > --- > arm/gic.c | 6 ------ > arm/kvm-cpu.c | 7 ++++++- > kvm-cpu.c | 7 +++++++ > 3 files changed, 13 insertions(+), 7 deletions(-) > > diff --git a/arm/gic.c b/arm/gic.c > index 99f0d2b..05f85a2 100644 > --- a/arm/gic.c > +++ b/arm/gic.c > @@ -84,12 +84,6 @@ int gic__create(struct kvm *kvm) > { > int err; > > - if (kvm->nrcpus > GIC_MAX_CPUS) { > - pr_warning("%d CPUS greater than maximum of %d -- truncating\n", > - kvm->nrcpus, GIC_MAX_CPUS); > - kvm->nrcpus = GIC_MAX_CPUS; > - } > - > /* Try the new way first, and fallback on legacy method otherwise */ > err = gic__create_device(kvm); > if (err) > diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c > index 7780251..b2fd6ed 100644 > --- a/arm/kvm-cpu.c > +++ b/arm/kvm-cpu.c > @@ -51,8 +51,13 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id) > return NULL; > > vcpu->vcpu_fd = ioctl(kvm->vm_fd, KVM_CREATE_VCPU, cpu_id); > - if (vcpu->vcpu_fd < 0) > + if (vcpu->vcpu_fd < 0) { > + if (errno == EINVAL) { > + free(vcpu); > + return NULL; > + } Hmm, but EINVAL can mean all sorts of other failures too, surely? I'm not against removing the nrcpus check, but I think we should die if ioctls start failing rather than silently ignore them. Will