From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751462AbdIEJLP (ORCPT ); Tue, 5 Sep 2017 05:11:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:49532 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750905AbdIEJLN (ORCPT ); Tue, 5 Sep 2017 05:11:13 -0400 Subject: Re: [PATCH resend] x86,kvm: Add a kernel parameter to disable PV spinlock To: Peter Zijlstra Cc: Davidlohr Bueso , Oscar Salvador , Ingo Molnar , Paolo Bonzini , "H . Peter Anvin" , Thomas Gleixner , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, Waiman Long References: <20170904142836.15446-1-osalvador@suse.de> <20170904144011.gp7hpis6usjehbuf@hirez.programming.kicks-ass.net> <20170904222157.GD17982@linux-80c1.suse> <0869e8a5-4abd-8f7f-0135-aab3e72e2d01@suse.com> <20170905065837.rs767a4os2aumg7h@hirez.programming.kicks-ass.net> <924fec17-548a-083d-edce-7adcb662c513@suse.com> <20170905081001.hn2276qrhfyqpjdi@hirez.programming.kicks-ass.net> <83ac209b-0807-0a72-cd07-d4ccd1d1ed61@suse.com> <20170905082801.d3sr7hdjz6lpon5p@hirez.programming.kicks-ass.net> <1b3afce5-c95d-5a3a-c36c-953a0654ab2d@suse.com> <20170905090306.gz52hlo7s2ybogoy@hirez.programming.kicks-ass.net> From: Juergen Gross Message-ID: Date: Tue, 5 Sep 2017 11:11:10 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20170905090306.gz52hlo7s2ybogoy@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: de-DE Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/09/17 11:03, Peter Zijlstra wrote: > On Tue, Sep 05, 2017 at 10:52:06AM +0200, Juergen Gross wrote: >>> Hmm, that might work. Could we somehow nop that call when >>> !X86_FEATURE_HYPERVISOR?, that saves native from having to do the call >>> and would be a win for everyone. >> >> So in fact we want a "always false" shortcut for bare metal and for any >> virtualization environment selecting bare metal behavior. >> >> I'll have a try. > > Right, so for native I think you can do this: > > > diff --git a/arch/x86/kernel/paravirt_patch_64.c b/arch/x86/kernel/paravirt_patch_64.c > index 11aaf1eaa0e4..4e9839001291 100644 > --- a/arch/x86/kernel/paravirt_patch_64.c > +++ b/arch/x86/kernel/paravirt_patch_64.c > @@ -21,6 +21,7 @@ DEF_NATIVE(, mov64, "mov %rdi, %rax"); > #if defined(CONFIG_PARAVIRT_SPINLOCKS) > DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%rdi)"); > DEF_NATIVE(pv_lock_ops, vcpu_is_preempted, "xor %rax, %rax"); > +DEF_NATIVE(pv_lock_ops, virt_spin_lock, "xor %rax, %rax"); > #endif > > unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len) > @@ -77,6 +78,13 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf, > goto patch_site; > } > goto patch_default; > + case PARAVIRT_PATCH(pv_lock_ops.virt_spin_lock): > + if (!this_cpu_has(X86_FEATURE_HYPERVISOR)) { > + start = start_pv_lock_ops_virt_spin_lock; > + end = end_pv_lock_ops_virt_spin_lock; > + goto patch_side; > + } > + goto patch_default; I'd rather add a test to paravirt_patch_default() similar to the _paravirt_ident_* cases for catching the Xen (and possibly KVM) cases, too. I just need to add _paravirt_zero_[32|64] functions I can use for bare metal and the nopvspin cases. Juergen