On 11/29/2017 09:18 AM, Roger Pau Monné wrote: > 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? 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? > 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. Right, but that's not what Juergen's second option is. IIUIC with that option Linux starts with zeropage already prepared. No shim in the kernel. -boris
