[PATCH v2 0/7] kvm: fix latent guest entry/exit bugs

[Mark Rutland]

Several architectures have latent bugs around guest entry/exit. This
series addresses those for:

	arm64, mips, riscv, s390, x86

However, I'm not sure how to address powerpc and could do with some help
there. I have build-tested the arm64, mips, riscv, s390, and x86 cases,
but I don't have a suitable HW setup to test these, so any review and/or
testing would be much appreciated.

Issues include:

1) Several architectures enable interrupts between guest_enter() and
   guest_exit(). As this period is an RCU extended quiescent state (EQS)
   this is unsound unless the irq entry code explicitly wakes RCU, which
   most architectures only do for entry from usersapce or idle.

   I believe this affects: arm64, riscv, s390

   I am not sure about powerpc.

2) Several architectures permit instrumentation of code between
   guest_enter() and guest_exit(), e.g. KASAN, KCOV, KCSAN, etc. As
   instrumentation may directly o indirectly use RCU, this has the same
   problems as with interrupts.

   I believe this affects: arm64, mips, powerpc, riscv, s390

3) Several architectures do not inform lockdep and tracing that
   interrupts are enabled during the execution of the guest, or do so in
   an incorrect order. Generally this means that logs will report IRQs
   being masked for much longer than is actually the case, which is not
   ideal for debugging. I don't know whether this affects the
   correctness of lockdep.

   I believe this affects: arm64, mips, powerpc, riscv, s390

This was previously fixed for x86 specifically in a series of commits:

  87fa7f3e98a1310e ("x86/kvm: Move context tracking where it belongs")
  0642391e2139a2c1 ("x86/kvm/vmx: Add hardirq tracing to guest enter/exit")
  9fc975e9efd03e57 ("x86/kvm/svm: Add hardirq tracing on guest enter/exit")
  3ebccdf373c21d86 ("x86/kvm/vmx: Move guest enter/exit into .noinstr.text")
  135961e0a7d555fc ("x86/kvm/svm: Move guest enter/exit into .noinstr.text")
  160457140187c5fb ("KVM: x86: Defer vtime accounting 'til after IRQ handling")
  bc908e091b326467 ("KVM: x86: Consolidate guest enter/exit logic to common helpers")

But other architectures were left broken, and the infrastructure for
handling this correctly is x86-specific.

This series introduces generic helper functions which can be used to
handle the problems above, and migrates architectures over to these,
fixing the latent issues. For s390, where the KVM guest EQS is
interruptible, I've added infrastructure to wake RCU during this EQS.

Since v1 [1]:
* Add arch_in_rcu_eqs()
* Convert s390
* Rename exit_to_guest_mode() -> guest_state_enter_irqoff()
* Rename enter_from_guest_mode() -> guest_state_exit_irqoff()
* Various commit message cleanups

I've pushed the series (based on v5.16) to my kvm/entry-rework branch:

  https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=kvm/entry-rework
  git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git kvm/entry-rework

... with this version tagged as kvm-entry-rework-20210119.

[1] https://lore.kernel.org/r/20220111153539.2532246-1-mark.rutland@xxxxxxx/

Thanks,
Mark.

Mark Rutland (7):
  entry: add arch_in_rcu_eqs()
  kvm: add guest_state_{enter,exit}_irqoff()
  kvm/arm64: rework guest entry logic
  kvm/mips: rework guest entry logic
  kvm/riscv: rework guest entry logic
  kvm/s390: rework guest entry logic
  kvm/x86: rework guest entry logic

 arch/arm64/kvm/arm.c                 |  51 +++++++-----
 arch/mips/kvm/mips.c                 |  37 ++++++++-
 arch/riscv/kvm/vcpu.c                |  44 +++++++----
 arch/s390/include/asm/entry-common.h |  10 +++
 arch/s390/include/asm/kvm_host.h     |   3 +
 arch/s390/kvm/kvm-s390.c             |  49 +++++++++---
 arch/s390/kvm/vsie.c                 |  17 ++--
 arch/x86/kvm/svm/svm.c               |   4 +-
 arch/x86/kvm/vmx/vmx.c               |   4 +-
 arch/x86/kvm/x86.c                   |   4 +-
 arch/x86/kvm/x86.h                   |  45 -----------
 include/linux/entry-common.h         |  16 ++++
 include/linux/kvm_host.h             | 112 ++++++++++++++++++++++++++-
 kernel/entry/common.c                |   3 +-
 14 files changed, 286 insertions(+), 113 deletions(-)

-- 
2.30.2