[PATCH 0/3] Pin the hrtimer used for VMX-preemption timer emulation

Jim Mattson
2020-05-08T20:36:54Z

I'm still not entirely convinced that the Linux hrtimer can be used to
accurately emulate the VMX-preemption timer, but it definitely doesn't
work if the hrtimer is on a different logical processor from the vCPU
thread that needs to get kicked out of VMX non-root operation.

With these changes, the kvm-unit-test (sent separately) that verifies
that a guest can't actually observe a delayed VMX-preemption timer
VM-exit passes 99.999% of the time on a 2GHz Skylake system.

It might be possible to improve that pass rate even more by increasing
the scaling factor in the virtual IA32_VMX_MISC[4:0], but you'd have
to be even more of a stickler than I to go to that extreme.

By the way, what is the point of migrating the hrtimers for the APIC
and the PIT, since they aren't even pinned to begin with?

The subject line of the first patch was crafted for you, Sean. :-D

Jim Mattson (3):
KVM: nVMX: Really make emulated nested preemption timer pinned
KVM: nVMX: Change emulated VMX-preemption timer hrtimer to absolute
KVM: nVMX: Migrate the VMX-preemption timer

arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/irq.c | 2 ++
arch/x86/kvm/vmx/nested.c | 5 +++--
arch/x86/kvm/vmx/vmx.c | 11 +++++++++++
4 files changed, 18 insertions(+), 2 deletions(-)

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2.26.2.645.ge9eca65c58-goog