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SubjectRe: [PATCH v7 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL
On Fri, Jul 12, 2019 at 04:29:06PM +0800, Tao Xu wrote:
> UMWAIT and TPAUSE instructions use IA32_UMWAIT_CONTROL at MSR index E1H
> to determines the maximum time in TSC-quanta that the processor can reside
> in either C0.1 or C0.2.
>
> This patch emulates MSR IA32_UMWAIT_CONTROL in guest and differentiate
> IA32_UMWAIT_CONTROL between host and guest. The variable
> mwait_control_cached in arch/x86/power/umwait.c caches the MSR value, so
> this patch uses it to avoid frequently rdmsr of IA32_UMWAIT_CONTROL.
>
> Co-developed-by: Jingqi Liu <jingqi.liu@intel.com>
> Signed-off-by: Jingqi Liu <jingqi.liu@intel.com>
> Signed-off-by: Tao Xu <tao3.xu@intel.com>
> ---
[...]
> +static void atomic_switch_umwait_control_msr(struct vcpu_vmx *vmx)
> +{
> + if (!vmx_has_waitpkg(vmx))
> + return;
> +
> + if (vmx->msr_ia32_umwait_control != umwait_control_cached)
> + add_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL,
> + vmx->msr_ia32_umwait_control,
> + umwait_control_cached, false);

How exactly do we ensure NR_AUTOLOAD_MSRS (8) is still large enough?

I see 3 existing add_atomic_switch_msr() calls, but the one at
atomic_switch_perf_msrs() is in a loop. Are we absolutely sure
that perf_guest_get_msrs() will never return more than 5 MSRs?


> + else
> + clear_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL);
> +}
> +
> static void vmx_arm_hv_timer(struct vcpu_vmx *vmx, u32 val)
> {
> vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, val);
[...]


--
Eduardo

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