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From: Kyle Huey <me@kylehuey.com>
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Subject: [PATCH v10 0/7] x86/arch_prctl Add ARCH_[GET|SET]_CPUID for controlling the CPUID instruction
Date: Tue,  8 Nov 2016 10:39:49 -0800
Message-Id: <20161108183956.4521-1-khuey@kylehuey.com>
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rr (http://rr-project.org/), a userspace record-and-replay reverse-
execution debugger, would like to trap and emulate the CPUID instruction.
This would allow us to a) mask away certain hardware features that rr does
not support (e.g. RDRAND) and b) enable trace portability across machines
by providing constant results.

Newer Intel CPUs (Ivy Bridge and later) can fault when CPUID is executed at
CPL > 0. Expose this capability to userspace as a new pair of arch_prctls,
ARCH_GET_CPUID and ARCH_SET_CPUID, with two values, ARCH_CPUID_ENABLE and
ARCH_CPUID_SIGSEGV.

Since v9:
Patch 7: KVM: x86: virtualize cpuid faulting
- Fixed wrong condition when testing for a hypervisor disabling cpuid
  faulting while it is active.
- Now stores MSRs as u64 for future extensibility.
- Added cpuid_fault_enabled and supports_cpuid_fault helper functions.
- Style nits.