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. > > Juergen > > > --- > > arch/x86/xen/enlighten_pvh.c | 74 ++++++++++++++++++++++++++++++++------------ > > 1 file changed, 55 insertions(+), 19 deletions(-) > > > > diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c > > index 98ab176..d93f711 100644 > > --- a/arch/x86/xen/enlighten_pvh.c > > +++ b/arch/x86/xen/enlighten_pvh.c > > @@ -31,21 +31,46 @@ static void xen_pvh_arch_setup(void) > > acpi_irq_model = ACPI_IRQ_MODEL_PLATFORM; > > } > > > > -static void __init init_pvh_bootparams(void) > > +static void __init init_pvh_bootparams(bool xen_guest) > > { > > struct xen_memory_map memmap; > > int rc; > > > > memset(&pvh_bootparams, 0, sizeof(pvh_bootparams)); > > > > - memmap.nr_entries = ARRAY_SIZE(pvh_bootparams.e820_table); > > - set_xen_guest_handle(memmap.buffer, pvh_bootparams.e820_table); > > - rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap); > > - if (rc) { > > - xen_raw_printk("XENMEM_memory_map failed (%d)\n", rc); > > - BUG(); > > + if (xen_guest) { > > + memmap.nr_entries = ARRAY_SIZE(pvh_bootparams.e820_table); > > + set_xen_guest_handle(memmap.buffer, pvh_bootparams.e820_table); > > + rc = HYPERVISOR_memory_op(XENMEM_memory_map, &memmap); > > + if (rc) { > > + xen_raw_printk("XENMEM_memory_map failed (%d)\n", rc); > > + BUG(); > > + } > > + pvh_bootparams.e820_entries = memmap.nr_entries; > > + } else if (pvh_start_info.nr_modules > 1) { > > + /* The second module should be the e820 data for KVM guests */ I don't think this is desirable. You might want to boot other OSes using this method, and they might want to pass more than one module. IMHO the hvm_start_info structure should be bumped to contain a pointer to the memory map. Note that there's a 'version' field that can be used for that. Even on Xen we might want to pass the memory map in such a way instead of using the hypercall. Thanks, Roger.
