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SubjectRe: [PATCH RESEND v3 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL
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On 6/16/2019 5:55 PM, 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>
> ---
> arch/x86/kvm/vmx/vmx.c | 36 ++++++++++++++++++++++++++++++++++++
> arch/x86/kvm/vmx/vmx.h | 3 +++
> arch/x86/power/umwait.c | 3 ++-
> 3 files changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b35bfac30a34..f33a25e82cb8 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1679,6 +1679,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> #endif
> case MSR_EFER:
> return kvm_get_msr_common(vcpu, msr_info);
> + case MSR_IA32_UMWAIT_CONTROL:
> + if (!vmx_waitpkg_supported())
> + return 1;
> +
> + msr_info->data = vmx->msr_ia32_umwait_control;
> + break;
> case MSR_IA32_SPEC_CTRL:
> if (!msr_info->host_initiated &&
> !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
> @@ -1841,6 +1847,15 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> return 1;
> vmcs_write64(GUEST_BNDCFGS, data);
> break;
> + case MSR_IA32_UMWAIT_CONTROL:
> + if (!vmx_waitpkg_supported())
> + return 1;
> +
> + if (!data)
> + break;
> +

Why cannot clear it to zero?

> + vmx->msr_ia32_umwait_control = data;
> + break;
> case MSR_IA32_SPEC_CTRL:
> if (!msr_info->host_initiated &&
> !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
> @@ -4126,6 +4141,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> vmx->rmode.vm86_active = 0;
> vmx->spec_ctrl = 0;
>
> + vmx->msr_ia32_umwait_control = 0;
> +
> vcpu->arch.microcode_version = 0x100000000ULL;
> vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
> kvm_set_cr8(vcpu, 0);
> @@ -6339,6 +6356,23 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
> msrs[i].host, false);
> }
>
> +static void atomic_switch_ia32_umwait_control(struct vcpu_vmx *vmx)
> +{
> + u64 host_umwait_control;
> +
> + if (!vmx_waitpkg_supported())
> + return;
> +
> + host_umwait_control = umwait_control_cached;
> +

It's redundant to define host_umwait_control and this line, we can just
use umwait_control_cached.

> + if (vmx->msr_ia32_umwait_control != host_umwait_control)
> + add_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL,
> + vmx->msr_ia32_umwait_control,
> + host_umwait_control, false);

The bit 1 is reserved, at least, we need to do below to ensure not
modifying the reserved bit:

guest_val = (vmx->msr_ia32_umwait_control & ~BIT_ULL(1)) |
(host_val & BIT_ULL(1))

> + 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);
> @@ -6447,6 +6481,8 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
>
> atomic_switch_perf_msrs(vmx);
>
> + atomic_switch_ia32_umwait_control(vmx);
> +
> vmx_update_hv_timer(vcpu);
>
> /*
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 61128b48c503..8485bec7c38a 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -14,6 +14,8 @@
> extern const u32 vmx_msr_index[];
> extern u64 host_efer;
>
> +extern u32 umwait_control_cached;
> +
> #define MSR_TYPE_R 1
> #define MSR_TYPE_W 2
> #define MSR_TYPE_RW 3
> @@ -194,6 +196,7 @@ struct vcpu_vmx {
> #endif
>
> u64 spec_ctrl;
> + u64 msr_ia32_umwait_control;
>
> u32 vm_entry_controls_shadow;
> u32 vm_exit_controls_shadow;
> diff --git a/arch/x86/power/umwait.c b/arch/x86/power/umwait.c
> index 7fa381e3fd4e..2e6ce4cbccb3 100644
> --- a/arch/x86/power/umwait.c
> +++ b/arch/x86/power/umwait.c
> @@ -9,7 +9,8 @@
> * MSR value. By default, umwait max time is 100000 in TSC-quanta and C0.2
> * is enabled
> */
> -static u32 umwait_control_cached = 100000;
> +u32 umwait_control_cached = 100000;
> +EXPORT_SYMBOL_GPL(umwait_control_cached);
>
> /*
> * Serialize access to umwait_control_cached and IA32_UMWAIT_CONTROL MSR
>

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