[0/2] x86: init improvements

Message

Roger Pau Monné May 2, 2023, 9:22 a.m. UTC

Hello,

The following series contain two minor improvements for early boot: the
first one is an alignment check when building the initial page tables,
the second is a consistency fix for the GDT used by the BSP for the
trampoline code.

Both are a result of some debugging work done on a system with broken
firmware that resulted in Xen text not being loaded at a 2Mb aligned
address.  This resulted in corrupted page tables that would manifest as
the ljmp from compatibility mode in trampoline_protmode_entry causing a
triple fault due to the GDT being located in the Xen text section, and
the page table entry for that address being corrupt because Xen was not
loaded a 2Mb boundary.

The aim of the series (specially the first patch) is not to allow
booting on such broken firmware, but to print an error message instead
of causing a triple fault.

Thanks, Roger.

Roger Pau Monne (2):
  x86/head: check base address alignment
  x86/trampoline: load the GDT located in the trampoline page

 xen/arch/x86/boot/head.S       | 9 +++++++++
 xen/arch/x86/boot/trampoline.S | 6 ++++++
 2 files changed, 15 insertions(+)