On Wed, Nov 29, 2017 at 03:11:12PM +0100, Juergen Gross wrote: > On 29/11/17 15:03, Boris Ostrovsky wrote: > > On 11/29/2017 03:50 AM, Roger Pau Monné wrote: > >> On Wed, Nov 29, 2017 at 09:21:59AM +0100, Juergen Gross wrote: > >>> On 28/11/17 20:34, Maran Wilson wrote: > >>>> For certain applications it is desirable to rapidly boot a KVM virtual > >>>> machine. In cases where legacy hardware and software support within the > >>>> guest is not needed, Qemu should be able to boot directly into the > >>>> uncompressed Linux kernel binary without the need to run firmware. > >>>> > >>>> There already exists an ABI to allow this for Xen PVH guests and the ABI is > >>>> supported by Linux and FreeBSD: > >>>> > >>>> https://xenbits.xen.org/docs/unstable/misc/hvmlite.html > >> I would also add a link to: > >> > >> http://xenbits.xen.org/docs/unstable/hypercall/x86_64/include,public,arch-x86,hvm,start_info.h.html#Struct_hvm_start_info > >> > >>>> This PoC patch enables Qemu to use that same entry point for booting KVM > >>>> guests. > >>>> > >>>> Even though the code is still PoC quality, I'm sending this as an RFC now > >>>> since there are a number of different ways the specific implementation > >>>> details can be handled. I chose a shared code path for Xen and KVM guests > >>>> but could just as easily create a separate code path that is advertised by > >>>> a different ELF note for KVM. There also seems to be some flexibility in > >>>> how the e820 table data is passed and how (or if) it should be identified > >>>> as e820 data. As a starting point, I've chosen the options that seem to > >>>> result in the smallest patch with minimal to no changes required of the > >>>> x86/HVM direct boot ABI. > >>> I like the idea. > >>> > >>> I'd rather split up the different hypervisor types early and use a > >>> common set of service functions instead of special casing xen_guest > >>> everywhere. This would make it much easier to support the KVM PVH > >>> boot without the need to configure the kernel with CONFIG_XEN. > >>> > >>> Another option would be to use the same boot path as with grub: set > >>> the boot params in zeropage and start at startup_32. > >> I think I prefer this approach since AFAICT it should allow for > >> greater code share with the common boot path. > > > > 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? But then it won't be using the PVH entry point, and would just use the native one? My understanding was that the PVH shim inside of Linux will prepare a zero-page when booted using the PVH entry point, and then jump into the native boot path. Roger.
