From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: Re: [PATCH 2/2] powerpc/kvm: Limit MAX_VCPUS for guests running on RT Linux Date: Wed, 18 Feb 2015 10:36:49 +0100 Message-ID: <54E45D31.3020302@linutronix.de> References: <1424251955-308-1-git-send-email-bogdan.purcareata@freescale.com> <1424251955-308-3-git-send-email-bogdan.purcareata@freescale.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, scottwood@freescale.com, mihai.caraman@freescale.com To: Bogdan Purcareata , linuxppc-dev@lists.ozlabs.org, linux-rt-users@vger.kernel.org, agraf@suse.de, pbonzini@redhat.com Return-path: In-Reply-To: <1424251955-308-3-git-send-email-bogdan.purcareata@freescale.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org On 02/18/2015 10:32 AM, Bogdan Purcareata wrote: > Due to the introduction of the raw_spinlock for the KVM openpic, guests with a > high number of VCPUs may induce great latencies on the underlying RT Linux > system (e.g. cyclictest reports latencies of ~15ms for guests with 24 VCPUs). > This can be further aggravated by sending a lot of external interrupts to the > guest. > > A malicious app can abuse this scenario, causing a DoS of the host Linux. > Until the KVM openpic code is refactored to use finer lock granularity, impose > a limitation on the number of VCPUs a guest can have when running on a > PREEMPT_RT_FULL system with KVM_MPIC emulation. How is this possible? You take the raw lock, write a register, release the raw lock. How can the guest lockup the host? Is this write blocking in guest? Sebastian