[PATCH 0/3] hvf x86 correctness and efficiency improvements

[Phil Dennis-Jordan]

This is a series of semi-related patches for the x86 macOS Hypervisor.framework
(hvf) accelerator backend. The intention is to make VMs run slightly more
efficiently on macOS host machines. They have been subject to some months of
CI workloads with macOS guest VMs without issues and they seem to give a few
percent performance improvement. (Though this varies greatly with the type of
workload.)

Patch 1 enables the INVTSC CPUID bit when running with hvf. This can enable
some optimisations in the guest OS, and I've not found any reason it shouldn't
be allowed for hvf based hosts.

Patch 2 fixes hvf_kick_vcpu_thread so it actually forces a VM exit instead of
doing nothing. I guess this previously didn't cause any huge issues because
hvf's hv_vcpu_run() would exit so extremely frequently on its own accord. The
temp variable is needed because the pointer expected by the hv_vcpu_interrupt()
call doesn't match the fd field's type in the hvf accel's struct AccelCPUState.
I'm unsure if it would be better to change that struct field to the relevant
architecture's handle types, hv_vcpuid_t (x86, unsigned int) and hv_vcpu_t
(aarch64, uint64_t), perhaps via an intermediate typedef?

Patch 3, which replaces the call to hv_vcpu_run() with the more modern
hv_vcpu_run_until() for running the guest vCPU. The newer API is available
from macOS 10.15 host systems onwards. This call causes significantly fewer
VM exits, which also means we really need that exit-forcing interrupt from
patch 2. The reduction in VM exits means less overhead from exits and less
contention on the BQL. Using hv_vcpu_run_until() is also a prerequisite for
using certain newer hvf features, though this patchset doesn't use any.

Patches 2 & 3 must therefore be applied in that order, patch 1 is independent.

This work has been sponsored by Sauce Labs Inc.

Phil Dennis-Jordan (3):
  i386: hvf: Adds support for INVTSC cpuid bit
  i386: hvf: In kick_vcpu use hv_vcpu_interrupt to force exit
  i386: hvf: Updates API usage to use modern vCPU run function

 target/i386/hvf/hvf.c       | 26 +++++++++++++++++++++++++-
 target/i386/hvf/x86_cpuid.c |  4 ++++
 2 files changed, 29 insertions(+), 1 deletion(-)

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2.36.1