Re: [PATCH 1/3] KVM: nVMX: Really make emulated nested preemption timer pinned

Sean Christopherson
2020-05-08T22:16:29Z

LOL, love the shortlog :-)

On Fri, May 08, 2020 at 01:36:41PM -0700, Jim Mattson wrote:
> The PINNED bit is ignored by hrtimer_init. It is only considered when
> starting the timer.
>
> When the hrtimer isn't pinned to the same logical processor as the
> vCPU thread to be interrupted, the emulated VMX-preemption timer
> often fails to adhere to the architectural specification.
>
> Fixes: f15a75eedc18e ("KVM: nVMX: make emulated nested preemption timer pinned")
> Signed-off-by: Jim Mattson <jmattson@google.com>
> Reviewed-by: Peter Shier <pshier@google.com>
> Reviewed-by: Oliver Upton <oupton@google.com>
> ---
> arch/x86/kvm/vmx/nested.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index fd78ffbde644..1f7fe6f47cbc 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2041,7 +2041,7 @@ static void vmx_start_preemption_timer(struct kvm_vcpu *vcpu)
> preemption_timeout *= 1000000;
> do_div(preemption_timeout, vcpu->arch.virtual_tsc_khz);
> hrtimer_start(&vmx->nested.preemption_timer,
> - ns_to_ktime(preemption_timeout), HRTIMER_MODE_REL);
> + ns_to_ktime(preemption_timeout), HRTIMER_MODE_REL_PINNED);
> }
>
> static u64 nested_vmx_calc_efer(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
> --
> 2.26.2.645.ge9eca65c58-goog
>