From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v7 06/13] KVM: x86: Add Intel Processor Trace virtualization mode Date: Thu, 3 May 2018 13:50:39 +0200 Message-ID: <47494e95-edcb-e8b5-0a32-004e9470dbdf@redhat.com> References: <1525349323-9938-1-git-send-email-luwei.kang@intel.com> <1525349323-9938-7-git-send-email-luwei.kang@intel.com> <20180503113223.x2ykby6wglppgdwf@um.fi.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, rkrcmar@redhat.com, linux-kernel@vger.kernel.org, joro@8bytes.org, peterz@infradead.org, chao.p.peng@linux.intel.com To: Alexander Shishkin , Luwei Kang Return-path: In-Reply-To: <20180503113223.x2ykby6wglppgdwf@um.fi.intel.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 03/05/2018 13:32, Alexander Shishkin wrote: >> >> +/* Default is SYSTEM mode. */ >> +static int __read_mostly pt_mode = PT_MODE_SYSTEM; >> +module_param(pt_mode, int, S_IRUGO); > So, it's an explicit module parameter? One apparent problem with this > is that one would need to reload kvm module(s) to be able to use PT, > which is not ideal. If you want to do tracing system-wide, that by definition must disable guest tracing, so I think the module parameter is appropriate. The question is more, what is the best default. Paolo