From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2001:470:1f0b:db:abcd:42:0:1]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 24A091A0A40 for ; Wed, 18 Feb 2015 21:09:47 +1100 (AEDT) Message-ID: <54E45D31.3020302@linutronix.de> Date: Wed, 18 Feb 2015 10:36:49 +0100 From: Sebastian Andrzej Siewior MIME-Version: 1.0 To: Bogdan Purcareata , linuxppc-dev@lists.ozlabs.org, linux-rt-users@vger.kernel.org, agraf@suse.de, pbonzini@redhat.com Subject: Re: [PATCH 2/2] powerpc/kvm: Limit MAX_VCPUS for guests running on RT Linux References: <1424251955-308-1-git-send-email-bogdan.purcareata@freescale.com> <1424251955-308-3-git-send-email-bogdan.purcareata@freescale.com> In-Reply-To: <1424251955-308-3-git-send-email-bogdan.purcareata@freescale.com> Content-Type: text/plain; charset=windows-1252 Cc: scottwood@freescale.com, mihai.caraman@freescale.com, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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