From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: AMD Ryzen KVM/NPT/IOMMU issue Date: Wed, 28 Jun 2017 22:33:45 +0200 Message-ID: References: <575f8fbc-0fdc-f336-e3da-53f27da4b2e1@markju.com> <20170505112706.7785948c@t450s.home> <545f19a3-4923-cdec-4ce9-2a4155a04f6a@amd.com> <5d2ea709-8f90-bfaa-975d-48aed39e75ad@amd.com> <20170628130855.76c2b700@w520.home> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Matthias Ehrenfeuchter To: Graham Neville , "Bridgman, John" Return-path: In-Reply-To: Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: kvm.vger.kernel.org On 28/06/2017 21:52, Graham Neville wrote: > Although not related to graphics card performance, there is definitely > another issue with regards to running KVM nested L2 guests when npt=1. > > Thought I'd mention this in case it helps with identifying performance > issues with NPT. > > I'm unable to start any L2 guests with KVM acceleration (--enable-kvm). > As soon as it attempts to bring up the L2 guest the L1 host crashes, L0 > host remains online. Nothing is printed in either L1 or L0's dmesg. > > My L0 is running Arch with 4.11.0-rc6, with qemu 2.8.0. I've tried > different L1 hosts (Ubuntu,Arch) and different kernels right to 4.12-rc5 > kernel, along with different qemu versions. > > This used to work fine with my Intel i7-4770s setup. > > With npt=0, L2 guests can start but performance is dier. Nested AMD needs some care. It's known, but time has been lacking... Paolo