From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [PATCH] KVM: SVM: obey guest PAT Date: Fri, 10 Nov 2017 22:27:19 +0100 Message-ID: <20171110212718.GA2189@flask> References: <20171026071327.15427-1-pbonzini@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, stable@vger.kernel.org To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <20171026071327.15427-1-pbonzini@redhat.com> Sender: stable-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 2017-10-26 09:13+0200, Paolo Bonzini: > For many years some users of assigned devices have reported worse > performance on AMD processors with NPT than on AMD without NPT, > Intel or bare metal. > > The reason turned out to be that SVM is discarding the guest PAT > setting and uses the default (PA0=PA4=WB, PA1=PA5=WT, PA2=PA6=UC-, > PA3=UC). The guest might be using a different setting, and > especially might want write combining but isn't getting it > (instead getting slow UC or UC- accesses). > > Thanks a lot to geoff@hostfission.com for noticing the relation > to the g_pat setting. The patch has been tested also by a bunch > of people on VFIO users forums. > > Fixes: 709ddebf81cb40e3c36c6109a7892e8b93a09464 > Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=196409 > Cc: stable@vger.kernel.org > Signed-off-by: Paolo Bonzini Applied, thanks.