linux-kernel - Re: [RFC PATCH] KVM: x86: Allow Qemu/KVM to use PVH entry point

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Date:   Wed, 29 Nov 2017 15:47:22 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Roger Pau Monné <roger.pau@...rix.com>
Cc:     Maran Wilson <maran.wilson@...cle.com>, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        rkrcmar@...hat.com, JBeulich@...e.com, andrew.cooper3@...rix.com,
        kvm@...r.kernel.org
Subject: Re: [RFC PATCH] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 29/11/17 15:44, Paolo Bonzini wrote:
> On 29/11/2017 15:25, Boris Ostrovsky wrote:
>>>>> 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?
> 
> QEMU is the right place to parse the ELF file and save it in memory.
> You would have to teach QEMU to find the Xen note in ELF-format kernels
> (just like it looks for the multiboot header), and use a different
> option ROM ("pvhboot.c" for example).
> 
> However I don't like to bypass the BIOS; for -kernel, KVM starts the
> guest with an option ROM (linuxboot-dma.c or multiboot.S in QEMU
> sources) that takes care of boot.
> 
> In either case, you would have a new option ROM.  It could either be
> very simple and similar to multiboot.S, or it could be larger and do the
> same task as xen-pvh.S and enlighten_pvh.c (then get the address of
> startup_32 or startup_64 from FW_CFG_KERNEL_ENTRY and jump there).  The
> ugly part is that the option ROM would have to know more details about
> what it is going to boot, including for example whether it's 32-bit or
> 64-bit, so I don't really think it is a good idea.

As grub2 doesn't have to know, qemu shouldn't have to know either.


Juergen