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

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Message-ID: <ba735c9c-5b51-2496-ce07-6fd37eec9d73@citrix.com>
Date:   Thu, 6 Dec 2018 23:36:27 +0000
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Maran Wilson <maran.wilson@...cle.com>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
        <kvm@...r.kernel.org>, <jgross@...e.com>
CC:     <thomas.lendacky@....com>, <dave.hansen@...ux.intel.com>,
        <rkrcmar@...hat.com>, <hpa@...or.com>, <mingo@...hat.com>,
        <rdunlap@...radead.org>, <luto@...nel.org>, <jpoimboe@...hat.com>,
        <tglx@...utronix.de>, <bp@...e.de>,
        <kirill.shutemov@...ux.intel.com>, <roger.pau@...rix.com>
Subject: Re: [Xen-devel] [PATCH v8 1/7] xen/pvh: Split CONFIG_XEN_PVH into
 CONFIG_PVH and CONFIG_XEN_PVH

On 06/12/2018 23:30, Paolo Bonzini wrote:
> On 07/12/18 00:11, Boris Ostrovsky wrote:
>> On 12/6/18 5:49 PM, Paolo Bonzini wrote:
>>> On 06/12/18 23:34, Boris Ostrovsky wrote:
>>>> On 12/6/18 5:11 PM, Paolo Bonzini wrote:
>>>>
>>>>> and also
>>>>>
>>>>> 	depends on !EFI
>>>>>
>>>>> because even though in principle it would be possible to write a PVH
>>>>> loader for UEFI, PVH's start info does not support the EFI handover
>>>>> protocol.
>>>> But we should be able to build the binary with both EFI and PVH?
>>> Can you?  It's a completely different binary format, the EFI handover
>>> protocol is invoked via a special entry point and needs the Linux header
>>> format, not ELF.
>> Right, but I think it is desirable to be able to build both from the
>> same config file.
> Ah, "make bzImage" and use the vmlinux for PVH, because PVH fetches the
> entry point from the special note.  That's clever. :)
>
> I don't see why it should not work, and if so the "depends on !EFI" is
> indeed unnecessary.

We do strive for single binaries in the Xen world, because that is how
people actually want to consume Xen.

It is for this reason why a single xen.gz binary can be loaded as a
straight ELF (including this PVH boot protocol), or via Multiboot 1 or
2, and even do full EFI if your bootloader is up to date on its
Multiboot2 spec :)

~Andrew