[RFC PATCH 0/4] KVM: Emulate UMIP (or almost do so)

From: Paolo Bonzini
Date: Tue Jul 12 2016 - 15:20:50 EST

UMIP (User-Mode Instruction Prevention) is a feature of future
Intel processors (Cannonlake?) that blocks SLDT, SGDT, STR, SIDT
and SMSW from user-mode processes.

The idea here is to use virtualization intercepts to emulate UMIP; it
slows down the instructions when they're executed in ring 0, but they
are really never executed in practice. On AMD systems it's possible
to emulate it entirely; instead on Intel systems it's *almost* possible
to emulate it, because SMSW doesn't cause a vmexit, and hence SMSW will
not fault.

This patch series provides the infrastructure and implements it on
Intel. I tested it through kvm-unit-tests.

Still I think the idea is interesting, even if it's buggy for current
Intel processors. Any opinions?


Paolo Bonzini (4):
x86: add UMIP feature and CR4 bit
KVM: x86: emulate sldt and str
KVM: x86: add support for emulating UMIP
KVM: vmx: add support for emulating UMIP

arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/kvm_host.h | 3 ++-
arch/x86/include/asm/vmx.h | 1 +
arch/x86/include/uapi/asm/processor-flags.h | 2 ++
arch/x86/include/uapi/asm/vmx.h | 4 +++
arch/x86/kvm/cpuid.c | 5 +++-
arch/x86/kvm/cpuid.h | 8 ++++++
arch/x86/kvm/emulate.c | 40 ++++++++++++++++++++++++-----
arch/x86/kvm/svm.c | 6 +++++
arch/x86/kvm/vmx.c | 40 ++++++++++++++++++++++++++++-
arch/x86/kvm/x86.c | 3 +++
11 files changed, 104 insertions(+), 9 deletions(-)