Re: [PATCH 5/5] KVM: nVMX: optimize prepare_vmcs02{,_full} for Enlightened VMCS case

From: Liran Alon
Date: Thu Jun 14 2018 - 19:37:49 EST

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----- vkuznets@xxxxxxxxxx wrote:

> When Enlightened VMCS is in use by L1 hypervisor we can avoid
> vmwriting
> VMCS fields which did not change.
>
> Our first goal is to achieve minimal impact on traditional VMCS case
> so
> we're not wrapping each vmwrite() with an if-changed checker. We also
> can't
> utilize static keys as Enlightened VMCS usage is per-guest.
>
> This patch implements the simpliest solution: checking fields in
> groups.
> We skip single vmwrite() statements as doing the check will cost us
> something even in non-evmcs case and the win is tiny. Unfortunately,
> this
> makes prepare_vmcs02_full{,_full}() code Enlightened VMCS-dependent
> (and
> a bit ugly).
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 143
> ++++++++++++++++++++++++++++++-----------------------
> 1 file changed, 82 insertions(+), 61 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 6802ba91468c..9a7d76c5c92b 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -11619,50 +11619,79 @@ static int nested_vmx_load_cr3(struct
> kvm_vcpu *vcpu, unsigned long cr3, bool ne
> return 0;
> }
>
> +/*
> + * Check if L1 hypervisor changed the particular field in
> Enlightened
> + * VMCS and avoid redundant vmwrite if it didn't. Can only be used
> when
> + * the value we're about to write is unchanged vmcs12->field.
> + */
> +#define evmcs_needs_write(vmx, clean_field)
> ((vmx)->nested.dirty_vmcs12 ||\
> + !(vmx->nested.hv_evmcs->hv_clean_fields &\
> + HV_VMX_ENLIGHTENED_CLEAN_FIELD_##clean_field))

Why declare this is a macro instead of an static inline small function?
Just to shorten the name of the clean-field constant?

> +
> static void prepare_vmcs02_full(struct kvm_vcpu *vcpu, struct vmcs12
> *vmcs12)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> + struct hv_enlightened_vmcs *hv_evmcs = vmx->nested.hv_evmcs;
> +
> + if (!hv_evmcs || evmcs_needs_write(vmx, GUEST_GRP2)) {
> + vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector);
> + vmcs_write16(GUEST_SS_SELECTOR, vmcs12->guest_ss_selector);
> + vmcs_write16(GUEST_DS_SELECTOR, vmcs12->guest_ds_selector);
> + vmcs_write16(GUEST_FS_SELECTOR, vmcs12->guest_fs_selector);
> + vmcs_write16(GUEST_GS_SELECTOR, vmcs12->guest_gs_selector);
> + vmcs_write16(GUEST_LDTR_SELECTOR, vmcs12->guest_ldtr_selector);
> + vmcs_write16(GUEST_TR_SELECTOR, vmcs12->guest_tr_selector);
> + vmcs_write32(GUEST_ES_LIMIT, vmcs12->guest_es_limit);
> + vmcs_write32(GUEST_SS_LIMIT, vmcs12->guest_ss_limit);
> + vmcs_write32(GUEST_DS_LIMIT, vmcs12->guest_ds_limit);
> + vmcs_write32(GUEST_FS_LIMIT, vmcs12->guest_fs_limit);
> + vmcs_write32(GUEST_GS_LIMIT, vmcs12->guest_gs_limit);
> + vmcs_write32(GUEST_LDTR_LIMIT, vmcs12->guest_ldtr_limit);
> + vmcs_write32(GUEST_TR_LIMIT, vmcs12->guest_tr_limit);
> + vmcs_write32(GUEST_GDTR_LIMIT, vmcs12->guest_gdtr_limit);
> + vmcs_write32(GUEST_IDTR_LIMIT, vmcs12->guest_idtr_limit);
> + vmcs_write32(GUEST_ES_AR_BYTES, vmcs12->guest_es_ar_bytes);
> + vmcs_write32(GUEST_SS_AR_BYTES, vmcs12->guest_ss_ar_bytes);
> + vmcs_write32(GUEST_DS_AR_BYTES, vmcs12->guest_ds_ar_bytes);
> + vmcs_write32(GUEST_FS_AR_BYTES, vmcs12->guest_fs_ar_bytes);
> + vmcs_write32(GUEST_GS_AR_BYTES, vmcs12->guest_gs_ar_bytes);
> + vmcs_write32(GUEST_LDTR_AR_BYTES, vmcs12->guest_ldtr_ar_bytes);
> + vmcs_write32(GUEST_TR_AR_BYTES, vmcs12->guest_tr_ar_bytes);
> + vmcs_writel(GUEST_SS_BASE, vmcs12->guest_ss_base);
> + vmcs_writel(GUEST_DS_BASE, vmcs12->guest_ds_base);
> + vmcs_writel(GUEST_FS_BASE, vmcs12->guest_fs_base);
> + vmcs_writel(GUEST_GS_BASE, vmcs12->guest_gs_base);
> + vmcs_writel(GUEST_LDTR_BASE, vmcs12->guest_ldtr_base);
> + vmcs_writel(GUEST_TR_BASE, vmcs12->guest_tr_base);
> + vmcs_writel(GUEST_GDTR_BASE, vmcs12->guest_gdtr_base);
> + vmcs_writel(GUEST_IDTR_BASE, vmcs12->guest_idtr_base);
> + }
> +
> + if (!hv_evmcs || evmcs_needs_write(vmx, GUEST_GRP1)) {
> + vmcs_write32(GUEST_SYSENTER_CS, vmcs12->guest_sysenter_cs);
> + vmcs_writel(GUEST_PENDING_DBG_EXCEPTIONS,
> + vmcs12->guest_pending_dbg_exceptions);
> + vmcs_writel(GUEST_SYSENTER_ESP, vmcs12->guest_sysenter_esp);
> + vmcs_writel(GUEST_SYSENTER_EIP, vmcs12->guest_sysenter_eip);
> +
> + if (vmx_mpx_supported())
> + vmcs_write64(GUEST_BNDCFGS, vmcs12->guest_bndcfgs);
>
> - vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector);
> - vmcs_write16(GUEST_SS_SELECTOR, vmcs12->guest_ss_selector);
> - vmcs_write16(GUEST_DS_SELECTOR, vmcs12->guest_ds_selector);
> - vmcs_write16(GUEST_FS_SELECTOR, vmcs12->guest_fs_selector);
> - vmcs_write16(GUEST_GS_SELECTOR, vmcs12->guest_gs_selector);
> - vmcs_write16(GUEST_LDTR_SELECTOR, vmcs12->guest_ldtr_selector);
> - vmcs_write16(GUEST_TR_SELECTOR, vmcs12->guest_tr_selector);
> - vmcs_write32(GUEST_ES_LIMIT, vmcs12->guest_es_limit);
> - vmcs_write32(GUEST_SS_LIMIT, vmcs12->guest_ss_limit);
> - vmcs_write32(GUEST_DS_LIMIT, vmcs12->guest_ds_limit);
> - vmcs_write32(GUEST_FS_LIMIT, vmcs12->guest_fs_limit);
> - vmcs_write32(GUEST_GS_LIMIT, vmcs12->guest_gs_limit);
> - vmcs_write32(GUEST_LDTR_LIMIT, vmcs12->guest_ldtr_limit);
> - vmcs_write32(GUEST_TR_LIMIT, vmcs12->guest_tr_limit);
> - vmcs_write32(GUEST_GDTR_LIMIT, vmcs12->guest_gdtr_limit);
> - vmcs_write32(GUEST_IDTR_LIMIT, vmcs12->guest_idtr_limit);
> - vmcs_write32(GUEST_ES_AR_BYTES, vmcs12->guest_es_ar_bytes);
> - vmcs_write32(GUEST_SS_AR_BYTES, vmcs12->guest_ss_ar_bytes);
> - vmcs_write32(GUEST_DS_AR_BYTES, vmcs12->guest_ds_ar_bytes);
> - vmcs_write32(GUEST_FS_AR_BYTES, vmcs12->guest_fs_ar_bytes);
> - vmcs_write32(GUEST_GS_AR_BYTES, vmcs12->guest_gs_ar_bytes);
> - vmcs_write32(GUEST_LDTR_AR_BYTES, vmcs12->guest_ldtr_ar_bytes);
> - vmcs_write32(GUEST_TR_AR_BYTES, vmcs12->guest_tr_ar_bytes);
> - vmcs_writel(GUEST_SS_BASE, vmcs12->guest_ss_base);
> - vmcs_writel(GUEST_DS_BASE, vmcs12->guest_ds_base);
> - vmcs_writel(GUEST_FS_BASE, vmcs12->guest_fs_base);
> - vmcs_writel(GUEST_GS_BASE, vmcs12->guest_gs_base);
> - vmcs_writel(GUEST_LDTR_BASE, vmcs12->guest_ldtr_base);
> - vmcs_writel(GUEST_TR_BASE, vmcs12->guest_tr_base);
> - vmcs_writel(GUEST_GDTR_BASE, vmcs12->guest_gdtr_base);
> - vmcs_writel(GUEST_IDTR_BASE, vmcs12->guest_idtr_base);
> -
> - vmcs_write32(GUEST_SYSENTER_CS, vmcs12->guest_sysenter_cs);
> - vmcs_writel(GUEST_PENDING_DBG_EXCEPTIONS,
> - vmcs12->guest_pending_dbg_exceptions);
> - vmcs_writel(GUEST_SYSENTER_ESP, vmcs12->guest_sysenter_esp);
> - vmcs_writel(GUEST_SYSENTER_EIP, vmcs12->guest_sysenter_eip);
> + /*
> + * L1 may access the L2's PDPTR, so save them to construct
> + * vmcs12
> + */
> + if (enable_ept) {
> + vmcs_write64(GUEST_PDPTR0, vmcs12->guest_pdptr0);
> + vmcs_write64(GUEST_PDPTR1, vmcs12->guest_pdptr1);
> + vmcs_write64(GUEST_PDPTR2, vmcs12->guest_pdptr2);
> + vmcs_write64(GUEST_PDPTR3, vmcs12->guest_pdptr3);
> + }
> + }
>
> if (nested_cpu_has_xsaves(vmcs12))
> vmcs_write64(XSS_EXIT_BITMAP, vmcs12->xss_exit_bitmap);
> +
> vmcs_write64(VMCS_LINK_POINTER, -1ull);
>
> if (cpu_has_vmx_posted_intr())
> @@ -11717,9 +11746,6 @@ static void prepare_vmcs02_full(struct
> kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>
> set_cr4_guest_host_mask(vmx);
>
> - if (vmx_mpx_supported())
> - vmcs_write64(GUEST_BNDCFGS, vmcs12->guest_bndcfgs);
> -
> if (enable_vpid) {
> if (nested_cpu_has_vpid(vmcs12) && vmx->nested.vpid02)
> vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->nested.vpid02);
> @@ -11727,16 +11753,6 @@ static void prepare_vmcs02_full(struct
> kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
> vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
> }
>
> - /*
> - * L1 may access the L2's PDPTR, so save them to construct vmcs12
> - */
> - if (enable_ept) {
> - vmcs_write64(GUEST_PDPTR0, vmcs12->guest_pdptr0);
> - vmcs_write64(GUEST_PDPTR1, vmcs12->guest_pdptr1);
> - vmcs_write64(GUEST_PDPTR2, vmcs12->guest_pdptr2);
> - vmcs_write64(GUEST_PDPTR3, vmcs12->guest_pdptr3);
> - }
> -
> if (cpu_has_vmx_msr_bitmap())
> vmcs_write64(MSR_BITMAP, __pa(vmx->nested.vmcs02.msr_bitmap));
> }
> @@ -11757,6 +11773,7 @@ static int prepare_vmcs02(struct kvm_vcpu
> *vcpu, struct vmcs12 *vmcs12,
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> u32 exec_control, vmcs12_exec_ctrl;
> + struct hv_enlightened_vmcs *hv_evmcs = vmx->nested.hv_evmcs;
>
> if (vmx->nested.dirty_vmcs12 || vmx->nested.hv_evmcs) {
> prepare_vmcs02_full(vcpu, vmcs12);
> @@ -11768,11 +11785,13 @@ static int prepare_vmcs02(struct kvm_vcpu
> *vcpu, struct vmcs12 *vmcs12,
> * with vmx_shadow_fields.h.
> */
>
> - vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector);
> - vmcs_write32(GUEST_CS_LIMIT, vmcs12->guest_cs_limit);
> - vmcs_write32(GUEST_CS_AR_BYTES, vmcs12->guest_cs_ar_bytes);
> - vmcs_writel(GUEST_ES_BASE, vmcs12->guest_es_base);
> - vmcs_writel(GUEST_CS_BASE, vmcs12->guest_cs_base);
> + if (!hv_evmcs || evmcs_needs_write(vmx, GUEST_GRP2)) {
> + vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector);
> + vmcs_write32(GUEST_CS_LIMIT, vmcs12->guest_cs_limit);
> + vmcs_write32(GUEST_CS_AR_BYTES, vmcs12->guest_cs_ar_bytes);
> + vmcs_writel(GUEST_ES_BASE, vmcs12->guest_es_base);
> + vmcs_writel(GUEST_CS_BASE, vmcs12->guest_cs_base);
> + }
>
> /*
> * Not in vmcs02: GUEST_PML_INDEX, HOST_FS_SELECTOR,
> HOST_GS_SELECTOR,
> @@ -11788,12 +11807,14 @@ static int prepare_vmcs02(struct kvm_vcpu
> *vcpu, struct vmcs12 *vmcs12,
> vmcs_write64(GUEST_IA32_DEBUGCTL, vmx->nested.vmcs01_debugctl);
> }
> if (vmx->nested.nested_run_pending) {
> - vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
> - vmcs12->vm_entry_intr_info_field);
> - vmcs_write32(VM_ENTRY_EXCEPTION_ERROR_CODE,
> - vmcs12->vm_entry_exception_error_code);
> - vmcs_write32(VM_ENTRY_INSTRUCTION_LEN,
> - vmcs12->vm_entry_instruction_len);
> + if (!hv_evmcs || evmcs_needs_write(vmx, CONTROL_EVENT)) {
> + vmcs_write32(VM_ENTRY_INTR_INFO_FIELD,
> + vmcs12->vm_entry_intr_info_field);
> + vmcs_write32(VM_ENTRY_EXCEPTION_ERROR_CODE,
> + vmcs12->vm_entry_exception_error_code);
> + vmcs_write32(VM_ENTRY_INSTRUCTION_LEN,
> + vmcs12->vm_entry_instruction_len);
> + }
> vmcs_write32(GUEST_INTERRUPTIBILITY_INFO,
> vmcs12->guest_interruptibility_info);
> vmx->loaded_vmcs->nmi_known_unmasked =
> --
> 2.14.4

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