[Qemu-devel] [RFC 0/2] target-arm: Provide '-cpu host' when running KVM

[Peter Maydell <peter.maydell@linaro.org>]

These patches add support to target-arm for '-cpu host'.
The general semantics are the same as for ppc and x86 (ie "whatever
the host kernel can support that looks basically like the host
CPU"), but the mechanism is a little different.

The kernel API (currently still proposed rather than implemented,
hence the RFC nature of this patchset) is that the existing
KVM_ARM_VCPU_INIT supports a new 'target' value KVM_ARM_TARGET_HOST,
which it treats as "whatever you are". On the userspace side,
we use this if the kernel supports it. If it doesn't then we
know the kernel must be an A15-on-A15 only one, and so can
safely implement '-cpu host' with KVM_ARM_TARGET_CORTEX_A15.

In order to find out details of the vCPU so we can correctly
set up our ARMCPU objects, we create a scratch VM and a single
cpu within it; we can then use the existing "read registers"
API to access the ID registers. We do this once at startup
when we register the new QOM type.

('-cpu host' is also going to be useful for AArch64 because
it gives us a path to providing KVM support without having
to implement a model of a specific v8 CPU and all its system
registers...)

Peter Maydell (2):
  target-arm: Don't hardcode KVM target CPU to be A15
  target-arm: Provide '-cpu host' when running KVM

 target-arm/helper.c |    6 ++
 target-arm/kvm.c    |  227 ++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 231 insertions(+), 2 deletions(-)

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1.7.9.5