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Commit 2fb92db1 authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: VMX: Cache vmcs segment fields 



Since the emulator now checks segment limits and access rights, it
generates a lot more accesses to the vmcs segment fields.  Undo some
of the performance hit by cacheing those fields in a read-only cache
(the entire cache is invalidated on any write, or on guest exit).

Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent 1aa36616

arch/x86/include/asm/kvm_host.h

+1 −0
Original line number Diff line number Diff line
@@ -136,6 +136,7 @@ enum kvm_reg_ex { 
	VCPU_EXREG_CR3,

	VCPU_EXREG_RFLAGS,

	VCPU_EXREG_CPL,

	VCPU_EXREG_SEGMENTS,

};



enum {

arch/x86/kvm/vmx.c

+92 −10
Original line number Diff line number Diff line
@@ -162,6 +162,10 @@ struct vcpu_vmx { 
			u32 ar;

		} tr, es, ds, fs, gs;

	} rmode;

	struct {

		u32 bitmask; /* 4 bits per segment (1 bit per field) */

		struct kvm_save_segment seg[8];

	} segment_cache;

	int vpid;

	bool emulation_required;
@@ -174,6 +178,15 @@ struct vcpu_vmx { 
	bool rdtscp_enabled;

};



enum segment_cache_field {

	SEG_FIELD_SEL = 0,

	SEG_FIELD_BASE = 1,

	SEG_FIELD_LIMIT = 2,

	SEG_FIELD_AR = 3,



	SEG_FIELD_NR = 4

};



static inline struct vcpu_vmx *to_vmx(struct kvm_vcpu *vcpu)

{

	return container_of(vcpu, struct vcpu_vmx, vcpu);
@@ -646,6 +659,62 @@ static void vmcs_set_bits(unsigned long field, u32 mask) 
	vmcs_writel(field, vmcs_readl(field) | mask);

}



static void vmx_segment_cache_clear(struct vcpu_vmx *vmx)

{

	vmx->segment_cache.bitmask = 0;

}



static bool vmx_segment_cache_test_set(struct vcpu_vmx *vmx, unsigned seg,

				       unsigned field)

{

	bool ret;

	u32 mask = 1 << (seg * SEG_FIELD_NR + field);



	if (!(vmx->vcpu.arch.regs_avail & (1 << VCPU_EXREG_SEGMENTS))) {

		vmx->vcpu.arch.regs_avail |= (1 << VCPU_EXREG_SEGMENTS);

		vmx->segment_cache.bitmask = 0;

	}

	ret = vmx->segment_cache.bitmask & mask;

	vmx->segment_cache.bitmask |= mask;

	return ret;

}



static u16 vmx_read_guest_seg_selector(struct vcpu_vmx *vmx, unsigned seg)

{

	u16 *p = &vmx->segment_cache.seg[seg].selector;



	if (!vmx_segment_cache_test_set(vmx, seg, SEG_FIELD_SEL))

		*p = vmcs_read16(kvm_vmx_segment_fields[seg].selector);

	return *p;

}



static ulong vmx_read_guest_seg_base(struct vcpu_vmx *vmx, unsigned seg)

{

	ulong *p = &vmx->segment_cache.seg[seg].base;



	if (!vmx_segment_cache_test_set(vmx, seg, SEG_FIELD_BASE))

		*p = vmcs_readl(kvm_vmx_segment_fields[seg].base);

	return *p;

}



static u32 vmx_read_guest_seg_limit(struct vcpu_vmx *vmx, unsigned seg)

{

	u32 *p = &vmx->segment_cache.seg[seg].limit;



	if (!vmx_segment_cache_test_set(vmx, seg, SEG_FIELD_LIMIT))

		*p = vmcs_read32(kvm_vmx_segment_fields[seg].limit);

	return *p;

}



static u32 vmx_read_guest_seg_ar(struct vcpu_vmx *vmx, unsigned seg)

{

	u32 *p = &vmx->segment_cache.seg[seg].ar;



	if (!vmx_segment_cache_test_set(vmx, seg, SEG_FIELD_AR))

		*p = vmcs_read32(kvm_vmx_segment_fields[seg].ar_bytes);

	return *p;

}



static void update_exception_bitmap(struct kvm_vcpu *vcpu)

{

	u32 eb;
@@ -1271,9 +1340,11 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data) 
		break;

#ifdef CONFIG_X86_64

	case MSR_FS_BASE:

		vmx_segment_cache_clear(vmx);

		vmcs_writel(GUEST_FS_BASE, data);

		break;

	case MSR_GS_BASE:

		vmx_segment_cache_clear(vmx);

		vmcs_writel(GUEST_GS_BASE, data);

		break;

	case MSR_KERNEL_GS_BASE:
@@ -1717,6 +1788,8 @@ static void enter_pmode(struct kvm_vcpu *vcpu) 
	vmx->emulation_required = 1;

	vmx->rmode.vm86_active = 0;



	vmx_segment_cache_clear(vmx);



	vmcs_write16(GUEST_TR_SELECTOR, vmx->rmode.tr.selector);

	vmcs_writel(GUEST_TR_BASE, vmx->rmode.tr.base);

	vmcs_write32(GUEST_TR_LIMIT, vmx->rmode.tr.limit);
@@ -1740,6 +1813,8 @@ static void enter_pmode(struct kvm_vcpu *vcpu) 
	fix_pmode_dataseg(VCPU_SREG_GS, &vmx->rmode.gs);

	fix_pmode_dataseg(VCPU_SREG_FS, &vmx->rmode.fs);



	vmx_segment_cache_clear(vmx);



	vmcs_write16(GUEST_SS_SELECTOR, 0);

	vmcs_write32(GUEST_SS_AR_BYTES, 0x93);
@@ -1803,6 +1878,8 @@ static void enter_rmode(struct kvm_vcpu *vcpu) 
		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);

	}



	vmx_segment_cache_clear(vmx);



	vmx->rmode.tr.selector = vmcs_read16(GUEST_TR_SELECTOR);

	vmx->rmode.tr.base = vmcs_readl(GUEST_TR_BASE);

	vmcs_writel(GUEST_TR_BASE, rmode_tss_base(vcpu->kvm));
@@ -1879,6 +1956,8 @@ static void enter_lmode(struct kvm_vcpu *vcpu) 
{

	u32 guest_tr_ar;



	vmx_segment_cache_clear(to_vmx(vcpu));



	guest_tr_ar = vmcs_read32(GUEST_TR_AR_BYTES);

	if ((guest_tr_ar & AR_TYPE_MASK) != AR_TYPE_BUSY_64_TSS) {

		printk(KERN_DEBUG "%s: tss fixup for long mode. \n",
@@ -2082,7 +2161,6 @@ static void vmx_get_segment(struct kvm_vcpu *vcpu, 
			    struct kvm_segment *var, int seg)

{

	struct vcpu_vmx *vmx = to_vmx(vcpu);

	struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];

	struct kvm_save_segment *save;

	u32 ar;
@@ -2104,13 +2182,13 @@ static void vmx_get_segment(struct kvm_vcpu *vcpu, 
		var->limit = save->limit;

		ar = save->ar;

		if (seg == VCPU_SREG_TR

		    || var->selector == vmcs_read16(sf->selector))

		    || var->selector == vmx_read_guest_seg_selector(vmx, seg))

			goto use_saved_rmode_seg;

	}

	var->base = vmcs_readl(sf->base);

	var->limit = vmcs_read32(sf->limit);

	var->selector = vmcs_read16(sf->selector);

	ar = vmcs_read32(sf->ar_bytes);

	var->base = vmx_read_guest_seg_base(vmx, seg);

	var->limit = vmx_read_guest_seg_limit(vmx, seg);

	var->selector = vmx_read_guest_seg_selector(vmx, seg);

	ar = vmx_read_guest_seg_ar(vmx, seg);

use_saved_rmode_seg:

	if ((ar & AR_UNUSABLE_MASK) && !emulate_invalid_guest_state)

		ar = 0;
@@ -2127,14 +2205,13 @@ static void vmx_get_segment(struct kvm_vcpu *vcpu, 


static u64 vmx_get_segment_base(struct kvm_vcpu *vcpu, int seg)

{

	struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];

	struct kvm_segment s;



	if (to_vmx(vcpu)->rmode.vm86_active) {

		vmx_get_segment(vcpu, &s, seg);

		return s.base;

	}

	return vmcs_readl(sf->base);

	return vmx_read_guest_seg_base(to_vmx(vcpu), seg);

}



static int __vmx_get_cpl(struct kvm_vcpu *vcpu)
@@ -2146,7 +2223,7 @@ static int __vmx_get_cpl(struct kvm_vcpu *vcpu) 
	    && (kvm_get_rflags(vcpu) & X86_EFLAGS_VM)) /* if virtual 8086 */

		return 3;



	return vmcs_read16(GUEST_CS_SELECTOR) & 3;

	return vmx_read_guest_seg_selector(to_vmx(vcpu), VCPU_SREG_CS) & 3;

}



static int vmx_get_cpl(struct kvm_vcpu *vcpu)
@@ -2188,6 +2265,8 @@ static void vmx_set_segment(struct kvm_vcpu *vcpu, 
	struct kvm_vmx_segment_field *sf = &kvm_vmx_segment_fields[seg];

	u32 ar;



	vmx_segment_cache_clear(vmx);



	if (vmx->rmode.vm86_active && seg == VCPU_SREG_TR) {

		vmcs_write16(sf->selector, var->selector);

		vmx->rmode.tr.selector = var->selector;
@@ -2229,7 +2308,7 @@ static void vmx_set_segment(struct kvm_vcpu *vcpu, 


static void vmx_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l)

{

	u32 ar = vmcs_read32(GUEST_CS_AR_BYTES);

	u32 ar = vmx_read_guest_seg_ar(to_vmx(vcpu), VCPU_SREG_CS);



	*db = (ar >> 14) & 1;

	*l = (ar >> 13) & 1;
@@ -2816,6 +2895,8 @@ static int vmx_vcpu_reset(struct kvm_vcpu *vcpu) 
	if (ret != 0)

		goto out;



	vmx_segment_cache_clear(vmx);



	seg_setup(VCPU_SREG_CS);

	/*

	 * GUEST_CS_BASE should really be 0xffff0000, but VT vm86 mode
@@ -4188,6 +4269,7 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) 
				  | (1 << VCPU_EXREG_RFLAGS)

				  | (1 << VCPU_EXREG_CPL)

				  | (1 << VCPU_EXREG_PDPTR)

				  | (1 << VCPU_EXREG_SEGMENTS)

				  | (1 << VCPU_EXREG_CR3));

	vcpu->arch.regs_dirty = 0;