From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933071AbeBLI6j (ORCPT ); Mon, 12 Feb 2018 03:58:39 -0500 Received: from mail.cn.fujitsu.com ([183.91.158.132]:46674 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932630AbeBLI6h (ORCPT ); Mon, 12 Feb 2018 03:58:37 -0500 X-IronPort-AV: E=Sophos;i="5.43,368,1503331200"; d="scan'208";a="37000793" Subject: Re: [PATCH v3 0/5] x86/apic: Fix restoring boot irq mode in reboot and kexec/kdump To: "Eric W. Biederman" CC: Baoquan He , , , , , , , References: <20180209121008.28980-1-bhe@redhat.com> <87wozi7pwy.fsf@xmission.com> From: Dou Liyang Message-ID: <3bff2f47-ae3e-58e0-420a-378ff3f55b65@cn.fujitsu.com> Date: Mon, 12 Feb 2018 16:58:33 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <87wozi7pwy.fsf@xmission.com> Content-Type: text/plain; charset="gbk"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.106] X-yoursite-MailScanner-ID: 5705748AE766.A9E97 X-yoursite-MailScanner: Found to be clean X-yoursite-MailScanner-From: douly.fnst@cn.fujitsu.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Eric, At 02/12/2018 01:11 PM, Eric W. Biederman wrote: > Dou Liyang writes: > >> Hi all, >> >> One thing confused me. >> >> The disconnect_bsp_APIC() may restore the interrupt delivery mode into >> virtual wire mode. it uses the vector F as the spurious interrput, But, >> IMO, using the vector 0xFF(SPURIOUS_APIC_VECTOR) may more suitable and >> will give us more detail. Why the disconnect_bsp_APIC() use vector F >> here? > > I would say this needs a documentation search before changing this. > > This code originates in: > 208fb93162d5 ("[PATCH] kexec: x86_64: restore apic virtual wire mode on shutdown") > > The example in the Multi-Processor Specification v1.4 shows setting > up the SPIV to vector 0x0f. > Thanks for your detailed explanation, I found the example A-1 in this spec. > I don't know what is canonical and what will interact best with DOS, > and that erra of setup. The vector 0x0f seems an odd choice as > it is below 0x20 putting it in the range of vectors that are > reserved for processor exceptions. > > The constant SPURIOUS_APIC_VECTOR is definitely not something we want > to be using at this point as that is a linux specific setting and used > when Linux is up and running. So it is completely inapplicable. > > This is all about restoring how the apics were configured at boot time > so it may be appropriate to copy and store this value, if it was not > architectural. > > At a practical level at this point I suspect we are ok as the setting > of the SPIV this way has not caused any known problems in the last > decade. If someone wants to dig through the archtectural documents > and the real world practice and find a better value and explain the > change I would not oppose it. Indeed, I understand. Thanks, dou > > All I know for certain is using the constant SPURIOUS_APIC_VECTOR > is completely inappropriate (as that constant is about how linux uses > vectors) and thus the patch below is wrong. > >> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c >> index 25ddf02598d2..550deaad6a9a 100644 >> --- a/arch/x86/kernel/apic/apic.c >> +++ b/arch/x86/kernel/apic/apic.c >> @@ -2130,7 +2130,7 @@ void disconnect_bsp_APIC(int virt_wire_setup) >> value = apic_read(APIC_SPIV); >> value &= ~APIC_VECTOR_MASK; >> value |= APIC_SPIV_APIC_ENABLED; >> - value |= 0xf; >> + value |= SPURIOUS_APIC_VECTOR; >> apic_write(APIC_SPIV, value); >> >> if (!virt_wire_setup) { >> > > Eric > > >