From 74a497fae754bd970ad0573c26d0a3c5e784fa0c Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 20 Dec 2017 13:55:39 +0100 Subject: [PATCH] KVM: nVMX: track dirty state of non-shadowed VMCS fields MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit VMCS12 fields that are not handled through shadow VMCS are rarely written, and thus they are also almost constant in the vmcs02. We can thus optimize prepare_vmcs02 by skipping all the work for non-shadowed fields in the common case. This patch introduces the (pretty simple) tracking infrastructure; the next patches will move work to prepare_vmcs02_full and save a few hundred clock cycles per VMRESUME on a Haswell Xeon E5 system: before after cpuid 14159 13869 vmcall 15290 14951 inl_from_kernel 17703 17447 outl_to_kernel 16011 14692 self_ipi_sti_nop 16763 15825 self_ipi_tpr_sti_nop 17341 15935 wr_tsc_adjust_msr 14510 14264 rd_tsc_adjust_msr 15018 14311 mmio-wildcard-eventfd:pci-mem 16381 14947 mmio-datamatch-eventfd:pci-mem 18620 17858 portio-wildcard-eventfd:pci-io 15121 14769 portio-datamatch-eventfd:pci-io 15761 14831 (average savings 748, stdev 460). Signed-off-by: Paolo Bonzini Signed-off-by: Radim Krčmář --- arch/x86/kvm/vmx.c | 29 ++++++++++++++++++++++++++++- arch/x86/kvm/vmx_shadow_fields.h | 6 ++++++ 2 files changed, 34 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 4530b2ba63b9..1cc787f63972 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -436,6 +436,7 @@ struct nested_vmx { * data hold by vmcs12 */ bool sync_shadow_vmcs; + bool dirty_vmcs12; bool change_vmcs01_virtual_x2apic_mode; /* L2 must run next, and mustn't decide to exit to L1. */ @@ -7623,8 +7624,10 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu) { unsigned long field; gva_t gva; + struct vcpu_vmx *vmx = to_vmx(vcpu); unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION); u32 vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO); + /* The value to write might be 32 or 64 bits, depending on L1's long * mode, and eventually we need to write that into a field of several * possible lengths. The code below first zero-extends the value to 64 @@ -7667,6 +7670,20 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu) return kvm_skip_emulated_instruction(vcpu); } + switch (field) { +#define SHADOW_FIELD_RW(x) case x: +#include "vmx_shadow_fields.h" + /* + * The fields that can be updated by L1 without a vmexit are + * always updated in the vmcs02, the others go down the slow + * path of prepare_vmcs02. + */ + break; + default: + vmx->nested.dirty_vmcs12 = true; + break; + } + nested_vmx_succeed(vcpu); return kvm_skip_emulated_instruction(vcpu); } @@ -7681,6 +7698,7 @@ static void set_current_vmptr(struct vcpu_vmx *vmx, gpa_t vmptr) __pa(vmx->vmcs01.shadow_vmcs)); vmx->nested.sync_shadow_vmcs = true; } + vmx->nested.dirty_vmcs12 = true; } /* Emulate the VMPTRLD instruction */ @@ -10297,6 +10315,11 @@ static int nested_vmx_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3, bool ne return 0; } +static void prepare_vmcs02_full(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12, + bool from_vmentry) +{ +} + /* * prepare_vmcs02 is called when the L1 guest hypervisor runs its nested * L2 guest. L1 has a vmcs for L2 (vmcs12), and this function "merges" it @@ -10592,7 +10615,6 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12, vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid); vmx_flush_tlb(vcpu, true); } - } if (enable_pml) { @@ -10641,6 +10663,11 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12, /* Note: modifies VM_ENTRY/EXIT_CONTROLS and GUEST/HOST_IA32_EFER */ vmx_set_efer(vcpu, vcpu->arch.efer); + if (vmx->nested.dirty_vmcs12) { + prepare_vmcs02_full(vcpu, vmcs12, from_vmentry); + vmx->nested.dirty_vmcs12 = false; + } + /* Shadow page tables on either EPT or shadow page tables. */ if (nested_vmx_load_cr3(vcpu, vmcs12->guest_cr3, nested_cpu_has_ept(vmcs12), entry_failure_code)) diff --git a/arch/x86/kvm/vmx_shadow_fields.h b/arch/x86/kvm/vmx_shadow_fields.h index 31d7a15338ac..cd0c75f6d037 100644 --- a/arch/x86/kvm/vmx_shadow_fields.h +++ b/arch/x86/kvm/vmx_shadow_fields.h @@ -17,6 +17,12 @@ * (e.g. force a sync if VM_INSTRUCTION_ERROR is modified * by nested_vmx_failValid) * + * When adding or removing fields here, note that shadowed + * fields must always be synced by prepare_vmcs02, not just + * prepare_vmcs02_full. + */ + +/* * Keeping the fields ordered by size is an attempt at improving * branch prediction in vmcs_read_any and vmcs_write_any. */