linux-kernel - [PATCH 0/6] s390: improve speculative execution handling

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Date:   Wed, 17 Jan 2018 10:48:33 +0100
From:   Martin Schwidefsky <schwidefsky@...ibm.com>
To:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jon Masters <jcm@...hat.com>,
        Marcus Meissner <meissner@...e.de>,
        Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH 0/6] s390: improve speculative execution handling

This patch series implements multiple mitigations for the speculative
execution findings:
1. The definition of the gmb() barrier as currently used by the
   distributions, we may have to find a better name for it
2. The architecture code for the nospec interfaces, the macros for
   nospec_ptr and nospec_load just use the gmb() barrier
3. The enablement for firmware features to switch between different
   branch prediction modes. It comes with a config option
   CONFIG_KERNEL_NOBP, two new kernel parameters "nobp=[0|1]" and
   "nospec", and a new system call s390_modify_bp.
   With CONFIG_KERNEL_NOBP=y the new branch prediction mode is active
   for the kernel code by default and can be switched off with "nospec"
   or "nobp=0". With CONFIG_KERNEL_NOBP=n the new mode is inactive for
   kernel code unless "nobp=1" is specified.
   User space code can use the trapdoor system call s390_modify_bp to
   set the new TIF_NOBP bit. This switches to the new branch prediction
   mode for the lifetime of the task, any children of the task will
   inherit this attribute.
   The vCPU of a KVM guest will run with the new branch prediction
   mode if either the associated qemu task has TIF_NOBP set or if the
   KVM kernel code sets TIF_NOBP_GUEST. The later will require a small
   update to KVM backend.
4. Transport channel reduction by clearing registers on interrupts,
   system calls and KVM guest exits.

We are working on an equivalent for retpoline, stay tuned.

@Greg: I have started with the backports for the stable kernel releases,
but unless the interface for gmp/nospec_ptr/nospec_load is cast in stone
does it make sense to send them?

Christian Borntraeger (1):
  KVM: s390: wire up seb feature

Martin Schwidefsky (5):
  s390/alternative: use a copy of the facility bit mask
  s390: implement nospec_[load|ptr]
  s390: add options to change branch prediction behaviour for the kernel
  s390: add system call to run tasks with modified branch prediction
  s390: scrub registers on kernel entry and KVM exit

 arch/s390/Kconfig                   |  17 +++++
 arch/s390/include/asm/barrier.h     |  38 ++++++++++
 arch/s390/include/asm/facility.h    |  18 +++++
 arch/s390/include/asm/kvm_host.h    |   3 +-
 arch/s390/include/asm/lowcore.h     |   3 +-
 arch/s390/include/asm/processor.h   |   1 +
 arch/s390/include/asm/thread_info.h |   4 ++
 arch/s390/include/uapi/asm/kvm.h    |   4 +-
 arch/s390/include/uapi/asm/unistd.h |   3 +-
 arch/s390/kernel/alternative.c      |  33 ++++++++-
 arch/s390/kernel/early.c            |   5 ++
 arch/s390/kernel/entry.S            | 134 +++++++++++++++++++++++++++++++++++-
 arch/s390/kernel/ipl.c              |   1 +
 arch/s390/kernel/setup.c            |   4 +-
 arch/s390/kernel/smp.c              |   6 +-
 arch/s390/kernel/sys_s390.c         |   8 +++
 arch/s390/kernel/syscalls.S         |   1 +
 arch/s390/kvm/kvm-s390.c            |  11 +++
 arch/s390/kvm/vsie.c                |   8 +++
 include/uapi/linux/kvm.h            |   1 +
 20 files changed, 294 insertions(+), 9 deletions(-)

-- 
2.7.4