Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 29 Nov 2017 14:18:10 +0000
From:   Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>
To:     Juergen Gross <jgross@suse.com>
CC:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Maran Wilson <maran.wilson@oracle.com>, <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>
Subject: Re: [RFC PATCH] KVM: x86: Allow Qemu/KVM to use PVH entry point
Message-ID: <20171129141810.q3s3xflsflpjovdd@MacBook-Pro-de-Roger.local>
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>
MIME-Version: 1.0
Content-Type: text/plain; charset="iso-8859-1"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <0162f2cd-2d9e-1c89-bb8e-7ac0089f0b3a@suse.com>
User-Agent: NeoMutt/20171027
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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 Monn� 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?

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.

Roger.

From 1585410480125748463@xxx Wed Nov 29 14:20:55 +0000 2017
X-GM-THRID: 1585339868639162159
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread