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. -boris
