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

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Date: Wed, 10 Apr 2024 15:48:45 -0400
From: Jason Andryuk <jason.andryuk@....com>
To: Juergen Gross <jgross@...e.com>, Boris Ostrovsky
	<boris.ostrovsky@...cle.com>, Thomas Gleixner <tglx@...utronix.de>, "Ingo
 Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>, Stefano Stabellini <sstabellini@...nel.org>, "Oleksandr
 Tyshchenko" <oleksandr_tyshchenko@...m.com>, Paolo Bonzini
	<pbonzini@...hat.com>
CC: <xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>, "Jason
 Andryuk" <jason.andryuk@....com>
Subject: [PATCH 0/5] x86/pvh: Make PVH entry relocatable

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

-- 
2.44.0