[RFC,v2,0/7] Clean up x86_64 boot code

Message

David Woodhouse May 1, 2019, 7:39 p.m. UTC

Some cleanups for the boot path, originally inspired by an attempt to
avoid scribbling on arbitrarily-chosen low memory.

In the no-real-mode case we don't need to bounce through low memory at
all; we can run the 32-bit trampoline in-place in the Xen image.

The variables containing information which is optionally discovered by
the real-mode boot code can be put back in place in the Xen image and we
can dispense with the bootsym() pointer gymnastics in C code which
access them in low memory.

Next up is killing reloc(), which AFAICT only exists to ensure that
the various breadcrumbs left all over the place by the Multiboot
bootloader aren't scribbled on when we copy the 16-bit boot trampoline
into low memory. Except that it's copying it out of the way... into
the top of low memory. Suspect if I tell kexec to put a segment there,
it's going to fail quite horribly.

Which leaves me with no valid reason for reloc() to be running this
early, so I may well kill it with fire too. I just need to find a
safe location for the 16-bit boot code.

v2: Fix wake code. Thanks Andy for testing.

David Woodhouse (7):
  x86/wakeup: Stop using %fs for lidt/lgdt
  x86/boot: Remove gratuitous call back into low-memory code
  x86/boot: Only jump into low trampoline code for real-mode boot
  x86/boot: Split bootsym() into four types of relocations
  x86/boot: Rename trampoline_{start,end} to boot_trampoline_{start,end}
  x86/boot: Copy 16-bit boot variables back up to Xen image
  x86/boot: Do not use trampoline for no-real-mode boot paths

 xen/arch/x86/acpi/power.c         |   6 +-
 xen/arch/x86/boot/edd.S           |  18 ++--
 xen/arch/x86/boot/head.S          |  89 ++++++++++++------
 xen/arch/x86/boot/mem.S           |  35 +++-----
 xen/arch/x86/boot/trampoline.S    | 145 +++++++++++++++++++++++-------
 xen/arch/x86/boot/video.S         |  36 ++++----
 xen/arch/x86/boot/wakeup.S        |  23 ++---
 xen/arch/x86/cpu/common.c         |   2 +-
 xen/arch/x86/cpu/intel.c          |   2 +-
 xen/arch/x86/efi/efi-boot.h       |  31 +------
 xen/arch/x86/mm.c                 |   2 +-
 xen/arch/x86/platform_hypercall.c |  18 ++--
 xen/arch/x86/setup.c              |  72 ++++++++++++---
 xen/arch/x86/smpboot.c            |   6 +-
 xen/arch/x86/tboot.c              |   6 +-
 xen/arch/x86/x86_64/mm.c          |   2 +-
 xen/arch/x86/xen.lds.S            |  27 ++++--
 xen/include/asm-x86/acpi.h        |   2 +-
 xen/include/asm-x86/config.h      |  10 +--
 xen/include/asm-x86/e820.h        |   5 +-
 xen/include/asm-x86/edd.h         |   1 -
 21 files changed, 339 insertions(+), 199 deletions(-)

Comments

David Woodhouse May 1, 2019, 7:46 p.m. UTC | #1

Argh, that's the first version again. Sorry. The fixed version is in 
http://git.infradead.org/users/dwmw2/xen.git/shortlog/refs/heads/bootcleanup
but I won't post the whole series again right now.