[v2,0/5] x86/pvh: Make 64bit PVH entry relocatable

Message

Jason Andryuk Aug. 14, 2024, 7:50 p.m. UTC

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.

v2 addresses review feedback.  It also replace LOAD_PHYSICAL_ADDR with
_pa(pvh_start_xen) in some offset calculations.  They happened to be
equal in my original builds.  When the two values differ,
_pa(pvh_start_xen) is the correct one to use.

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 header
  x86/pvh: Add 64bit relocation page tables

 arch/x86/include/asm/pgtable_64.h |  23 ++++-
 arch/x86/kernel/head_64.S         |  20 ----
 arch/x86/platform/pvh/head.S      | 161 +++++++++++++++++++++++++++---
 include/xen/interface/elfnote.h   |  93 ++++++++++++++++-
 4 files changed, 259 insertions(+), 38 deletions(-)