[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH 0/3] x86/pvh: Support relocating dom0 kernel
On Thu, Mar 07, 2024 at 11:08:37AM +0100, Jan Beulich wrote: > On 07.03.2024 11:00, Roger Pau Monné wrote: > > On Wed, Mar 06, 2024 at 01:50:29PM -0500, Jason Andryuk wrote: > >> Xen tries to load a PVH dom0 kernel at the fixed guest physical address > >> from the elf headers. For Linux, this defaults to 0x1000000 (16MB), but > >> it can be configured. > >> > >> Unfortunately there exist firmwares that have reserved regions at this > >> address, so Xen fails to load the dom0 kernel since it's not RAM. > >> > >> The other issue is that the Linux PVH entry point is not > >> position-independent. It expects to run at the compiled > >> CONFIG_PHYSICAL_ADDRESS. > >> > >> This patch set expands the PVH dom0 builder to try to relocate the > >> kernel if needed and possible. XENFEAT_pvh_relocatable is added for > >> kernels to indicate they are relocatable. However, we may want to > >> switch to an additional ELF note with the kernel alignment. Linux > >> specifies a kernel alignment in the bzImage boot_params.setup_header, > >> but that is not present the ELF vmlinux file. > > > > I wonder whether we need a pair of notes, to signal the min/max > > addresses the kernel supports being relocated to. > > Plus, as per your other reply, a 3rd one to specify alignment needs. Alignment we could in theory get from the ELF program header, if OSes fill those reliably. FreeBSD seems to do so, haven't checked Linux. > Then again - a single note can have multiple values. So perhaps it > doesn't need to be more than one new notes (except if dealing with > multi-value ones is deemed too complicated). I've never dealt with a multi-value note, if that's not overly complicated I would be fine with it, otherwise multiple notes are OK IMO. Thanks, Roger.
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