From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2FFA0C4332F for ; Tue, 20 Dec 2022 12:43:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233708AbiLTMnO (ORCPT ); Tue, 20 Dec 2022 07:43:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46188 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233572AbiLTMms (ORCPT ); Tue, 20 Dec 2022 07:42:48 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C99BB1A81D for ; Tue, 20 Dec 2022 04:39:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671539928; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=2YGLPYrhUM3liQYpN3p/+bDVBoiicBenOmdXkygbdC0=; b=LXDEEGFr2NiW0tHm7TOAuFUfYCvdyxpv3v+YV19EwolWYJLGXiJDlTspVrIUC2if0wn03E LM9uCzN38oQymBy4hTGCQQEMlQmvtwS9j+MKUjEYGgjzVPYA4bfdyBLVfT3Zv5vrHCh0U6 v0qoZERRx21OGgKE8SEIfPyLxMx8D9A= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-561-hvM0dMytMiWl0AERQdiC_g-1; Tue, 20 Dec 2022 07:38:44 -0500 X-MC-Unique: hvM0dMytMiWl0AERQdiC_g-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 04002183B3C3; Tue, 20 Dec 2022 12:38:44 +0000 (UTC) Received: from localhost (ovpn-12-53.pek2.redhat.com [10.72.12.53]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 30D8240C201B; Tue, 20 Dec 2022 12:38:42 +0000 (UTC) Date: Tue, 20 Dec 2022 20:38:39 +0800 From: Baoquan He To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , x86@kernel.org, kexec@lists.infradead.org, dgilbert@redhat.com Subject: Re: [PATCH] Revert "x86/apic/x2apic: Implement IPI shorthands support" Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/20/22 at 12:38pm, Peter Zijlstra wrote: > On Tue, Dec 20, 2022 at 01:34:58PM +0800, Baoquan He wrote: > > This reverts commit 43931d350f30c6cd8c2f498d54ef7d65750abc92. > > > > On kvm guest with 4 cpus deployed, when adding 'nr_cpus=2' to normal > > kernel's cmdline, and triggering crash to jump to kdump kernel, kdump > > kernel will stably hang. Reverting commit 43931d350f30 ("x86/apic/x2apic: > > Implement IPI shorthands support") can fix it. > > > > The problem will disappear if removing 'nr_cpus=2' from normal kerne's > > cmdline. > > And the root cause for this is... ? Does the kvm x2apic emulation > somehow get upset when we shorthand CPUs that haven't been initialized? Thanks for checking. I haven't figure out the root cause. I haven't read the apic code for long time, and not familiar with the kvm code. So raise the issue to upstream. I can do testing if any suggestion. Add our virt dev Dr. David Alan Gilbert to CC.