Messages in this thread | | | Subject | Re: [Xen-devel] [PATCH v1 04/12] xen/hvmlite: Bootstrap HVMlite guest | From | Boris Ostrovsky <> | Date | Mon, 25 Jan 2016 10:08:55 -0500 |
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On 01/22/2016 07:30 PM, Andrew Cooper wrote: > On 22/01/2016 23:32, Luis R. Rodriguez wrote: >> On Fri, Jan 22, 2016 at 04:35:50PM -0500, Boris Ostrovsky wrote: >>> + /* >>> + * See Documentation/x86/boot.txt. >>> + * >>> + * Version 2.12 supports Xen entry point but we will use default x86/PC >>> + * environment (i.e. hardware_subarch 0). >>> + */ >>> + xen_hvmlite_boot_params.hdr.version = 0x212; >>> + xen_hvmlite_boot_params.hdr.type_of_loader = 9; /* Xen loader */ >>> +} >> I realize PV got away with setting up boot_params on C code but best >> ask now that this new code is being introduced: why can't we just have >> the Xen hypervisor fill this in? It'd save us all this code. > I agree that this looks to be a mess. Having said that, the DMLite boot > protocol is OS agnostic, and will be staying that way. > > It happens to look suspiciously like multiboot; a flat 32bit protected > mode entry (at a location chosen in an ELF note), with %ebx pointing to > an in-ram structure containing things like a command line and module list. > > I would have though the correct way to do direct Linux support would be > to have a very small init stub which constructs an appropriate zero > page, and lets the native entry point get on with things.
Which is really what hvmlite_start_xen()->xen_prepare_hvmlite()->hvmlite_bootparams() is doing. Not much more than that (for 64-bit it also loads identity mapping because that's what startup_64 wants)
-boris
> > This covers the usecase where people wish to boot a specific Linux > kernel straight out of the dom0 filesystem. > > For the alternative usecase of general OS support, dom0 would boot > something such as grub2 as the DMLite "kernel", at which point all > stooging around in the guests filesystem is done from guest context, > rather than control context (mitigating a substantial attack surface). > > ~Andrew
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