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Re: [Xen-devel]qemu-dm: direct kernel boot to HVM regression

To: Chun Yan Liu <cyliu@xxxxxxxxxx>
Subject: Re: [Xen-devel]qemu-dm: direct kernel boot to HVM regression
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Fri, 1 Apr 2011 16:12:12 +0100
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On Fri, 1 Apr 2011, Chun Yan Liu wrote:
> Direct kernel boot to HVM doesn't work in xen-4.0.1-testing and xen-4.1.0-
> testing. In xen-3.3.1-testing, it works.
> There were two patches related to this:
> Daniel P. Berrange's patch: 
> # Direct linux kernel boot for HVM, add a fake boot sector to first disk.
> # http://lists.xensource.com/archives/html/xen-devel/2007-12/msg00723.html
> xen-3.3.1-testing uses this patch and works.
> Anthony Liguori's patch:
> # use option rom instead of boot sector for -kernel
> # http://copilotco.com/mail-archives/qemu.2008/msg10186.html
> xen-4.0.1-testing and later adopts that. 
> It moves load_linux part to #ifndef CONFIG_DM case only:
> load_linux(phys_ram_base + option_rom_offset, kernel_filename, 
> initrd_filename, kernel_cmdline)
> But in a usual case, CONFIG_DM is set, that part of code is never executed. 
> Direct kernel boot to HVM doesn't work any more. It still calls bios to find 
> bootable disk.

I wasn't even aware that xen supported this feature for HVM guests.
How is it exposed to users? Why is this better than using PV guests?

> And another question: 
> when I tried to move load_linux outside the #ifndef CONFIG_DM check, the code 
> could not be built succcessfully. It complains qemu_ram_alloc is undefined 
> reference. Removing CONFIG_DM form xen-config-host.h and let it enter the 
> #ifndef CONFIG_DM part, there is same complain.
> qemu_ram_alloc is defined in tools/ioemu/exec.c, but I didn't find exec.o is 
> built. Not very clear about the make rules of that part, any info? 

You need to provide a qemu_ram_alloc implementation that is compiled and
works on xen, the default one wouldn't do it.
Maybe you can give a look at what we were doing in qemu-xen 3.3 and
forward-port it.
In any case you should be aware that we are about to switch to upstream
qemu for development on xen-unstable.

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