linux-kernel - Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and CONFIG_XEN

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Date:   Fri, 7 Dec 2018 14:50:46 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Maran Wilson <maran.wilson@...cle.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        boris.ostrovsky@...cle.com, jpoimboe@...hat.com,
        kirill.shutemov@...ux.intel.com, bp@...e.de,
        thomas.lendacky@....com, luto@...nel.org,
        dave.hansen@...ux.intel.com, roger.pau@...rix.com,
        rkrcmar@...hat.com, rdunlap@...radead.org
Subject: Re: [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into CONFIG_PVH and
 CONFIG_XEN_PVH

On 07/12/2018 14:41, Paolo Bonzini wrote:
> On 07/12/18 07:02, Juergen Gross wrote:
>> On 06/12/2018 23:11, Paolo Bonzini wrote:
>>> On 06/12/18 07:04, Maran Wilson wrote:
>>>> +config PVH
>>>> +	bool "Support for running PVH guests"
>>>> +	---help---
>>>> +	  This option enables the PVH entry point for guest virtual machines
>>>> +	  as specified in the x86/HVM direct boot ABI.
>>>> +
>>>
>>> IIUC this breaks "normal" bzImage boot, so we should have something like
>>>
>>> 	The resulting kernel will not boot with most x86 boot loaders
>>> 	such as GRUB or SYSLINUX.  Unless you plan to start the kernel
>>> 	using QEMU or Xen, you probably want to say N here.
>>
>> The resulting kernel should be able to be booted either in PVH mode
>> via the PVH entry point or the "normal" way via the still existing
>> old entry point(s).
>>
>> It is an _additional_ way to boot the kernel, not an exclusive
>> alternative.
> 
> Yup, understood now.  Different binaries but one build.

The PVH boot entry is in the same bzImage binary as the normal one.
Its just another entry, similar to the Xen PV boot entry. So the binary
arch/x86/boot/bzimage can be booted either on bare metal via grub2 or
other boot-loaders, as Xen PV-guest, as Xen PVH-guest, or as KVM
PVH-guest. So one build and one binary. The non-standard boot entries
(PV- or PVH-node) are found via ELF-notes by the boot loader (qemu in
case of KVM).


Juergen