From 58fbbf26eb01cf6d92cf18da8d14b3a4af9c4b47 Mon Sep 17 00:00:00 2001 From: Kevin Tian Date: Tue, 30 Aug 2011 13:56:17 +0300 Subject: [PATCH] KVM: APIC: avoid instruction emulation for EOI writes Instruction emulation for EOI writes can be skipped, since sane guest simply uses MOV instead of string operations. This is a nice improvement when guest doesn't support x2apic or hyper-V EOI support. a single VM bandwidth is observed with ~8% bandwidth improvement (7.4Gbps->8Gbps), by saving ~5% cycles from EOI emulation. Signed-off-by: Kevin Tian : Signed-off-by: Eddie Dong Signed-off-by: Marcelo Tosatti Signed-off-by: Avi Kivity --- arch/x86/include/asm/vmx.h | 12 ++++++++++++ arch/x86/kvm/lapic.c | 9 +++++++++ arch/x86/kvm/lapic.h | 1 + arch/x86/kvm/vmx.c | 21 +++++++++++++++++++++ 4 files changed, 43 insertions(+) diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h index 2caf290e989..31f180c21ce 100644 --- a/arch/x86/include/asm/vmx.h +++ b/arch/x86/include/asm/vmx.h @@ -350,6 +350,18 @@ enum vmcs_field { #define DEBUG_REG_ACCESS_REG(eq) (((eq) >> 8) & 0xf) /* 11:8, general purpose reg. */ +/* + * Exit Qualifications for APIC-Access + */ +#define APIC_ACCESS_OFFSET 0xfff /* 11:0, offset within the APIC page */ +#define APIC_ACCESS_TYPE 0xf000 /* 15:12, access type */ +#define TYPE_LINEAR_APIC_INST_READ (0 << 12) +#define TYPE_LINEAR_APIC_INST_WRITE (1 << 12) +#define TYPE_LINEAR_APIC_INST_FETCH (2 << 12) +#define TYPE_LINEAR_APIC_EVENT (3 << 12) +#define TYPE_PHYSICAL_APIC_EVENT (10 << 12) +#define TYPE_PHYSICAL_APIC_INST (15 << 12) + /* segment AR */ #define SEGMENT_AR_L_MASK (1 << 13) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 57dcbd4308f..52645f28387 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -864,6 +864,15 @@ static int apic_mmio_write(struct kvm_io_device *this, return 0; } +void kvm_lapic_set_eoi(struct kvm_vcpu *vcpu) +{ + struct kvm_lapic *apic = vcpu->arch.apic; + + if (apic) + apic_reg_write(vcpu->arch.apic, APIC_EOI, 0); +} +EXPORT_SYMBOL_GPL(kvm_lapic_set_eoi); + void kvm_free_lapic(struct kvm_vcpu *vcpu) { if (!vcpu->arch.apic) diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h index 52c9e6b9e72..82872432d47 100644 --- a/arch/x86/kvm/lapic.h +++ b/arch/x86/kvm/lapic.h @@ -26,6 +26,7 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu); void kvm_lapic_reset(struct kvm_vcpu *vcpu); u64 kvm_lapic_get_cr8(struct kvm_vcpu *vcpu); void kvm_lapic_set_tpr(struct kvm_vcpu *vcpu, unsigned long cr8); +void kvm_lapic_set_eoi(struct kvm_vcpu *vcpu); void kvm_lapic_set_base(struct kvm_vcpu *vcpu, u64 value); u64 kvm_lapic_get_base(struct kvm_vcpu *vcpu); void kvm_apic_set_version(struct kvm_vcpu *vcpu); diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 5e8d411b0a8..47419d6031e 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -71,6 +71,9 @@ module_param(vmm_exclusive, bool, S_IRUGO); static int __read_mostly yield_on_hlt = 1; module_param(yield_on_hlt, bool, S_IRUGO); +static int __read_mostly fasteoi = 1; +module_param(fasteoi, bool, S_IRUGO); + /* * If nested=1, nested virtualization is supported, i.e., guests may use * VMX and be a hypervisor for its own guests. If nested=0, guests may not @@ -4540,6 +4543,24 @@ static int handle_xsetbv(struct kvm_vcpu *vcpu) static int handle_apic_access(struct kvm_vcpu *vcpu) { + if (likely(fasteoi)) { + unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION); + int access_type, offset; + + access_type = exit_qualification & APIC_ACCESS_TYPE; + offset = exit_qualification & APIC_ACCESS_OFFSET; + /* + * Sane guest uses MOV to write EOI, with written value + * not cared. So make a short-circuit here by avoiding + * heavy instruction emulation. + */ + if ((access_type == TYPE_LINEAR_APIC_INST_WRITE) && + (offset == APIC_EOI)) { + kvm_lapic_set_eoi(vcpu); + skip_emulated_instruction(vcpu); + return 1; + } + } return emulate_instruction(vcpu, 0) == EMULATE_DONE; } -- 2.20.1