[PATCH 0/5] x86/pvh: Make PVH entry relocatable

Jason Andryuk
2024-04-10T19:48:58Z

Using the PVH entry point, the uncompressed vmlinux is loaded at
LOAD_PHYSICAL_ADDR, and execution starts in 32bit mode at the
address in XEN_ELFNOTE_PHYS32_ENTRY, pvh_start_xen, with paging
disabled.

Loading at LOAD_PHYSICAL_ADDR has not been a problem in the past as
virtual machines don't have conflicting memory maps. But Xen now
supports a PVH dom0, which uses the host memory map, and there are
Coreboot/EDK2 firmwares that have reserved regions conflicting with
LOAD_PHYSICAL_ADDR. Xen recently added XEN_ELFNOTE_PHYS32_RELOC to
specify an alignment, minimum and maximum load address when
LOAD_PHYSICAL_ADDR cannot be used. This patch series makes the PVH
entry path PIC to support relocation.

Only x86-64 is converted. The 32bit entry path calling into vmlinux,
which is not PIC, will not support relocation.

The entry path needs pages tables to switch to 64bit mode. A new
pvh_init_top_pgt is added to make the transition into the startup_64
when the regular init_top_pgt pagetables are setup. This duplication is
unfortunate, but it keeps the changes simpler. __startup_64() can't be
used to setup init_top_pgt for PVH entry because it is 64bit code - the
32bit entry code doesn't have page tables to use.

This is the straight forward implementation to make it work. Other
approaches could be pursued.

checkpatch.pl gives an error: "ERROR: Macros with multiple statements
should be enclosed in a do - while loop" about the moved PMDS macro.
But PMDS is an assembler macro, so its not applicable. There are some
false positive warnings "WARNING: space prohibited between function name
and open parenthesis '('" about the macro, too.

Jason Andryuk (5):
xen: sync elfnote.h from xen tree
x86/pvh: Make PVH entrypoint PIC for x86-64
x86/pvh: Set phys_base when calling xen_prepare_pvh()
x86/kernel: Move page table macros to new header
x86/pvh: Add 64bit relocation page tables

arch/x86/kernel/head_64.S | 22 +---
arch/x86/kernel/pgtable_64_helpers.h | 28 +++++
arch/x86/platform/pvh/head.S | 157 +++++++++++++++++++++++++--
include/xen/interface/elfnote.h | 93 +++++++++++++++-
4 files changed, 265 insertions(+), 35 deletions(-)
create mode 100644 arch/x86/kernel/pgtable_64_helpers.h

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2.44.0