Re: [Xen-devel] [Xen 4.12 bug] HVM/PVH boot confusion

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Wed, Jan 30, 2019 at 12:25:20PM +0100, Roger Pau Monné wrote:
> Adding Anthony who likely knows more about all this since it's closely
> related to QEMU.
> 
> On Tue, Jan 29, 2019 at 07:49:51PM +0000, Andrew Cooper wrote:
> > Hello,
> > 
> > Given the following vm.cfg file:
> > 
> > name="vm"
> > type="hvm"
> > 
> > vcpus=4
> > memory=1024
> > 
> > firmware_override="/root/xen-syms"
> > 
> > kernel="/boot/vmlinuz-4.4-xen"
> > ramdisk="/boot/initrd-4.4.0+10.img"
> 
> I know very little about direct kernel booting with HVM, but I assume
> using firmware_override gets rid of hvmloader and the BIOS/UEFI
> payload plus the option rom to direct boot into a Linux kernel?

In HVM direct boot case, SeaBIOS takes care of loading the kernel and
booting it. QEMU communicate with SeaBIOS via the firmware config
interface (fw_cfg).

Setting firmware_override only replace hvmloader by that other elf.


> So basically the module list is `mod[0] = kernel` and `mod[1] =
> ramdisk`?

No, the module list isn't magically change, I don't think.
The toolstack is still going to but seabios as one of the module
(probably only, I forgot), but there isn't a reason to put the
kernel/ramdisk in there.


In the config above, xen can be a kernel at most (I think), but
certainly not a firmware.

-- 
Anthony PERARD

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