On 07.03.2024 18:33, Jason Andryuk wrote: > On 2024-03-07 05:20, Roger Pau Monné wrote: >> 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. > > I will look into this more, but at first glance, I don't see a > connection between Linux's CONFIG_PHYSICAL_ALIGN and the values in the > elf headers. As a quick test, I set CONFIG_PHYSICAL_ALIGN=0x800000, but > the elf align values are still 0x200000. > > The elf header values may be a suitable fallback though?
Imo, given the above, explicit values should be required. Better not load a kernel than doing so and then getting hard to debug crashes. Jan
