[Xen-devel] [PATCH RFC v2 00/12] xen/x86: use per-vcpu stacks for 64 bit pv domains

[Juergen Gross <jgross@xxxxxxxx>]

As a preparation for doing page table isolation in the Xen hypervisor
in order to mitigate "Meltdown" use dedicated stacks, GDT and TSS for
64 bit PV domains mapped to the per-domain virtual area.

The per-vcpu stacks are used for early interrupt handling only. After
saving the domain's registers stacks are switched back to the normal
per physical cpu ones in order to be able to address on-stack data
from other cpus e.g. while handling IPIs.

Adding %cr3 switching between saving of the registers and switching
the stacks will enable the possibility to run guest code without any
per physical cpu mapping, i.e. avoiding the threat of a guest being
able to access other domains data.

Without any further measures it will still be possible for e.g. a
guest's user program to read stack data of another vcpu of the same
domain, but this can be easily avoided by a little PV-ABI modification
introducing per-cpu user address spaces.

This series is meant as a replacement for Andrew's patch series:
"x86: Prerequisite work for a Xen KAISER solution".

What needs to be done:
- verify livepatching is still working
- performance evaluation (Dario is working on it)
- the real page table switching


Changes since RFC V1:
- switch back to per physical cpu stacks in interrupt handling
- complete rework of series
- rebase to current staging
- adding reverts of Jan's band-aid patches
- adding two minor cleanups at the begin of the series
- done much more testing, including NMIs

Juergen Gross (12):
  x86: cleanup processor.h
  x86: don't use hypervisor stack size for dumping guest stacks
  x86: do a revert of e871e80c38547d9faefc6604532ba3e985e65873
  x86: revert 5784de3e2067ed73efc2fe42e62831e8ae7f46c4
  x86: don't access saved user regs via rsp in trap handlers
  x86: add a xpti command line parameter
  x86: allow per-domain mappings without NX bit or with specific mfn
  xen/x86: use dedicated function for tss initialization
  x86: enhance syscall stub to work in per-domain mapping
  x86: allocate per-vcpu stacks for interrupt entries
  x86: modify interrupt handlers to support stack switching
  x86: activate per-vcpu stacks in case of xpti

 docs/misc/xen-command-line.markdown |  16 +-
 xen/arch/x86/cpu/common.c           |  56 ++++---
 xen/arch/x86/domain.c               |  84 ++++++++--
 xen/arch/x86/mm.c                   | 102 ++++++++++---
 xen/arch/x86/pv/domain.c            | 161 +++++++++++++++++++-
 xen/arch/x86/smpboot.c              | 211 --------------------------
 xen/arch/x86/traps.c                |  26 ++--
 xen/arch/x86/x86_64/asm-offsets.c   |   6 +-
 xen/arch/x86/x86_64/compat/entry.S  |  98 ++++++------
 xen/arch/x86/x86_64/entry.S         | 295 ++++++++++++------------------------
 xen/arch/x86/x86_64/traps.c         |  47 +++---
 xen/common/wait.c                   |   8 +-
 xen/include/asm-x86/asm_defns.h     |  49 +++---
 xen/include/asm-x86/config.h        |  13 +-
 xen/include/asm-x86/current.h       |  71 ++++++---
 xen/include/asm-x86/desc.h          |   5 +
 xen/include/asm-x86/domain.h        |   5 +
 xen/include/asm-x86/mm.h            |   3 +
 xen/include/asm-x86/processor.h     |  42 -----
 xen/include/asm-x86/regs.h          |   2 +
 xen/include/asm-x86/system.h        |   8 +
 xen/include/asm-x86/x86_64/page.h   |   5 +-
 22 files changed, 647 insertions(+), 666 deletions(-)

-- 
2.13.6


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