From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755076AbdK2O0V (ORCPT ); Wed, 29 Nov 2017 09:26:21 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:31713 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750902AbdK2O0T (ORCPT ); Wed, 29 Nov 2017 09:26:19 -0500 Subject: Re: [RFC PATCH] KVM: x86: Allow Qemu/KVM to use PVH entry point To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Juergen Gross References: <1511897682-32060-1-git-send-email-maran.wilson@oracle.com> <176188ca-51f9-ef12-6e93-46ab2d8b8cfc@suse.com> <20171129085044.kc3yqqdcw3zmp2k2@MacBook-Pro-de-Roger.local> <4d213199-ea65-4410-5b7a-63038215e380@oracle.com> <0162f2cd-2d9e-1c89-bb8e-7ac0089f0b3a@suse.com> <20171129141810.q3s3xflsflpjovdd@MacBook-Pro-de-Roger.local> Cc: Maran Wilson , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, rkrcmar@redhat.com, JBeulich@suse.com, andrew.cooper3@citrix.com, pbonzini@redhat.com, kvm@vger.kernel.org From: Boris Ostrovsky Message-ID: <96f9b4a5-7cb6-19c3-227d-8c48916d5969@oracle.com> Date: Wed, 29 Nov 2017 09:25:50 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20171129141810.q3s3xflsflpjovdd@MacBook-Pro-de-Roger.local> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/29/2017 09:18 AM, Roger Pau Monné wrote: > On Wed, Nov 29, 2017 at 03:11:12PM +0100, Juergen Gross wrote: >> On 29/11/17 15:03, Boris Ostrovsky wrote: >>> On 11/29/2017 03:50 AM, Roger Pau Monné wrote: >>>> On Wed, Nov 29, 2017 at 09:21:59AM +0100, Juergen Gross wrote: >>>>> On 28/11/17 20:34, Maran Wilson wrote: >>>>>> For certain applications it is desirable to rapidly boot a KVM virtual >>>>>> machine. In cases where legacy hardware and software support within the >>>>>> guest is not needed, Qemu should be able to boot directly into the >>>>>> uncompressed Linux kernel binary without the need to run firmware. >>>>>> >>>>>> There already exists an ABI to allow this for Xen PVH guests and the ABI is >>>>>> supported by Linux and FreeBSD: >>>>>> >>>>>> https://xenbits.xen.org/docs/unstable/misc/hvmlite.html >>>> I would also add a link to: >>>> >>>> http://xenbits.xen.org/docs/unstable/hypercall/x86_64/include,public,arch-x86,hvm,start_info.h.html#Struct_hvm_start_info >>>> >>>>>> This PoC patch enables Qemu to use that same entry point for booting KVM >>>>>> guests. >>>>>> >>>>>> Even though the code is still PoC quality, I'm sending this as an RFC now >>>>>> since there are a number of different ways the specific implementation >>>>>> details can be handled. I chose a shared code path for Xen and KVM guests >>>>>> but could just as easily create a separate code path that is advertised by >>>>>> a different ELF note for KVM. There also seems to be some flexibility in >>>>>> how the e820 table data is passed and how (or if) it should be identified >>>>>> as e820 data. As a starting point, I've chosen the options that seem to >>>>>> result in the smallest patch with minimal to no changes required of the >>>>>> x86/HVM direct boot ABI. >>>>> I like the idea. >>>>> >>>>> I'd rather split up the different hypervisor types early and use a >>>>> common set of service functions instead of special casing xen_guest >>>>> everywhere. This would make it much easier to support the KVM PVH >>>>> boot without the need to configure the kernel with CONFIG_XEN. >>>>> >>>>> Another option would be to use the same boot path as with grub: set >>>>> the boot params in zeropage and start at startup_32. >>>> I think I prefer this approach since AFAICT it should allow for >>>> greater code share with the common boot path. >>> zeropage is x86/Linux-specific so we'd need some sort of firmware (like >>> grub) between a hypervisor and Linux to convert hvm_start_info to >>> bootparams. >> qemu? I think KVM folks didn't want to do this. I can't find the thread but I believe it was somewhere during Clear Containers discussion. Paolo? > But then it won't be using the PVH entry point, and would just use the > native one? > > My understanding was that the PVH shim inside of Linux will prepare a > zero-page when booted using the PVH entry point, and then jump into > the native boot path. Right, but that's not what Juergen's second option is. IIUIC with that option Linux starts with zeropage already prepared. No shim in the kernel. -boris