[v7,0/4] Make PAT handling less brittle

Message

Demi Marie Obenour Jan. 7, 2023, 10:07 p.m. UTC

While working on Qubes OS Marek found out that there were some PAT hacks
in the Linux i195 driver.  I decided to make Xen use Linux’s PAT to see
if it solved the graphics glitches that were observed; it did.  This
required a substantial amount of preliminary work that is useful even
without using Linux’s PAT.  Furthermore, it turned out that the graphics
glitches were due to a hardware bug, which means that Xen's PAT is
fundamentally incompatible with the use of current-generation Intel
integrated GPUs assigned to a PV guest (including dom0).

Patches 1 through 3 are the preliminary work.  Patch 3 does break ABI by
rejecting the unused PAT entries, but this will only impact buggy PV
guests and can be disabled with a Xen command-line option.  Patch 4
provides a new Kconfig option (CONFIG_LINUX_PAT) to use Linux's PAT
instead of Xen's default.

Only patches 3 and 4 actually change Xen’s observable behavior.  Patch 1
is strictly cleanup.  Patch 2 makes changing the PAT much less
error-prone, as problems with the PAT or with the associated _PAGE_*
constants will be detected at compile time.

Demi Marie Obenour (4):
  x86: Remove MEMORY_NUM_TYPES and NO_HARDCODE_MEM_TYPE
  x86/mm: Reject invalid cacheability in PV guests by default
  x86/mm: make code robust to future PAT changes
  x86: Allow using Linux's PAT

 docs/misc/xen-command-line.pandoc    |  11 ++
 xen/arch/x86/Kconfig                 |  33 ++++++
 xen/arch/x86/hvm/mtrr.c              |  18 ++--
 xen/arch/x86/include/asm/mtrr.h      |   2 -
 xen/arch/x86/include/asm/page.h      |  14 +++
 xen/arch/x86/include/asm/processor.h |  15 +++
 xen/arch/x86/include/asm/pv/domain.h |   7 ++
 xen/arch/x86/mm.c                    | 151 ++++++++++++++++++++++++++-
 xen/arch/x86/mm/shadow/multi.c       |   2 +-
 xen/arch/x86/pv/domain.c             |  18 +++-
 10 files changed, 255 insertions(+), 16 deletions(-)