From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3EF6A1957E4 for ; Thu, 12 Sep 2024 08:51:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726131108; cv=none; b=YxEKQPkOYzHkdIOH0h+IKY8bMJBVzDNN//Ozd3rAAq7TVlVxFVcOLAYkKkYcxf3qBCsyH9nz6Z4tIVyD7sQrWWs7L5ijFqTRbd/1LHbdUv0ta2a2E3EupjaxQ5ju4sPVI7adg80HVCXA1gMwLL1SFg95309tqdGNiNXxZjl1Np8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726131108; c=relaxed/simple; bh=jrzdkvA2k4V7QhoZu0ZT4M7IkYxu0cJc/66f2zTK70Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=sCR7oVOLQOuX3i/y3uYdJCCxk/9U1Actjdz0YHBq12Onr3TGUs9keESRDFD92Dag5SEiRRd1WY+n/ipbGXw+Hh0vbjmn2dp1i7xveSG/OlDF2bqDEkVu1AqkH+7HQe3ul5KseWIfeBLvf7fDS9X7nZFIEpI+eQPIdmcLsKYMobQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=1dkR+Ke+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="1dkR+Ke+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4CD87C4CEC5; Thu, 12 Sep 2024 08:51:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1726131107; bh=jrzdkvA2k4V7QhoZu0ZT4M7IkYxu0cJc/66f2zTK70Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=1dkR+Ke+mmMe9jtLyh+fEzu+w5pNPMTCbdN3ke94ntZVfjcpNuKFeKkEDarx4Fd+q c1d1F0e1VR4Oc1Z2p5Bw8+oURplxbBvr6+NcX5f8gjJ1Lx5WPE8jZ+bbfpw3Rgb7DM iyroyZn6ksKzBuLENM/PCxGoIJpGLMb3gEJi+ABs= Date: Thu, 12 Sep 2024 10:51:44 +0200 From: Greg KH To: Niels Dettenbach Cc: Thomas Gleixner , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , stable@vger.kernel.org Subject: Re: [PATCH 1/1] x86: SMP broken on Xen PV DomU since 6.9 Message-ID: <2024091235-degree-drinkable-5363@gregkh> References: <5998315.MhkbZ0Pkbq@gongov> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5998315.MhkbZ0Pkbq@gongov> On Thu, Sep 12, 2024 at 10:48:14AM +0200, Niels Dettenbach wrote: > Virtual machines under Xen Hypervisor (DomU) running in Xen PV mode use a > special, nonstandard synthetized CPU topology which "just works" under > kernels 6.9.x while newer kernels wrongly assuming a "crash kernel" and > disable SMP (reducing to one CPU core) because the newer topology > implementation produces a wrong error "[Firmware Bug]: APIC enumeration > order not specification compliant" after new topology checks which are > improper for Xen PV platform. As a result, the kernel disables SMT and > activates just one CPU core within the VM (DomU). > > The patch disables the regarding checks if it is running in Xen PV > mode (only) and bring back SMP / all CPUs as in the past to such DomU > VMs. > > Signed-off-by: Niels Dettenbach > > --- > > > The current behaviour leads all of our production Xen Host platforms > (amd64 - HPE proliant) unusable after updating to newer linux kernels > (with just one CPU available/activated per VM) while older kernels and > other OS (current NetBSD PV DomU) still work fully (and stable since many > years on the platform). > > Xen PV mode is still provided by current Xen and widely used - even > if less wide as the newer Xen PVH mode today. So a solution probably > will be required. > > So we assume that bug affects stable@vger.kernel.org as well. > This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly.