Commit 58fbbf26 authored by Kevin Tian's avatar Kevin Tian Committed by Avi Kivity
Browse files

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: default avatarKevin Tian <kevin.tian@intel.com>
<Based on earlier work from>:
Signed-off-by: default avatarEddie Dong <eddie.dong@intel.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 45133eca

arch/x86/include/asm/vmx.h

+12 −0
Original line number Diff line number Diff line
@@ -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)

arch/x86/kvm/lapic.c

+9 −0
Original line number Diff line number Diff line
@@ -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)

arch/x86/kvm/lapic.h

+1 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/kvm/vmx.c

+21 −0
Original line number Diff line number Diff line
@@ -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;

}

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