Commit a75beee6 authored by Eddie Dong's avatar Eddie Dong Committed by Avi Kivity
Browse files

KVM: VMX: Avoid saving and restoring msrs on lightweight vmexit 



In a lightweight exit (where we exit and reenter the guest without
scheduling or exiting to userspace in between), we don't need various
msrs on the host, and avoiding shuffling them around reduces raw exit
time by 8%.

i386 compile fix by Daniel Hecken <dh@bahntechnik.de>.

Signed-off-by: default avatarYaozu (Eddie) Dong <eddie.dong@intel.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent b3f37707

drivers/kvm/kvm.h

+4 −0
Original line number Diff line number Diff line
@@ -288,6 +288,10 @@ struct kvm_vcpu { 
	u64 apic_base;

	u64 ia32_misc_enable_msr;

	int nmsrs;

	int save_nmsrs;

#ifdef CONFIG_X86_64

	int msr_offset_kernel_gs_base;

#endif

	struct vmx_msr_entry *guest_msrs;

	struct vmx_msr_entry *host_msrs;

drivers/kvm/vmx.c

+72 −56
Original line number Diff line number Diff line
@@ -85,19 +85,6 @@ static const u32 vmx_msr_index[] = { 
};

#define NR_VMX_MSR ARRAY_SIZE(vmx_msr_index)



#ifdef CONFIG_X86_64

static unsigned msr_offset_kernel_gs_base;

#define NR_64BIT_MSRS 4

/*

 * avoid save/load MSR_SYSCALL_MASK and MSR_LSTAR by std vt

 * mechanism (cpu bug AA24)

 */

#define NR_BAD_MSRS 2

#else

#define NR_64BIT_MSRS 0

#define NR_BAD_MSRS 0

#endif



static inline int is_page_fault(u32 intr_info)

{

	return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VECTOR_MASK |
@@ -118,12 +105,22 @@ static inline int is_external_interrupt(u32 intr_info) 
		== (INTR_TYPE_EXT_INTR | INTR_INFO_VALID_MASK);

}



static struct vmx_msr_entry *find_msr_entry(struct kvm_vcpu *vcpu, u32 msr)

static int __find_msr_index(struct kvm_vcpu *vcpu, u32 msr)

{

	int i;



	for (i = 0; i < vcpu->nmsrs; ++i)

		if (vcpu->guest_msrs[i].index == msr)

			return i;

	return -1;

}



static struct vmx_msr_entry *find_msr_entry(struct kvm_vcpu *vcpu, u32 msr)

{

	int i;



	i = __find_msr_index(vcpu, msr);

	if (i >= 0)

		return &vcpu->guest_msrs[i];

	return NULL;

}
@@ -307,10 +304,10 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu) 


#ifdef CONFIG_X86_64

	if (is_long_mode(vcpu)) {

		save_msrs(vcpu->host_msrs + msr_offset_kernel_gs_base, 1);

		load_msrs(vcpu->guest_msrs, NR_BAD_MSRS);

		save_msrs(vcpu->host_msrs + vcpu->msr_offset_kernel_gs_base, 1);

	}

#endif

	load_msrs(vcpu->guest_msrs, vcpu->save_nmsrs);

}



static void vmx_load_host_state(struct kvm_vcpu *vcpu)
@@ -337,12 +334,8 @@ static void vmx_load_host_state(struct kvm_vcpu *vcpu) 


		reload_tss();

	}

#ifdef CONFIG_X86_64

	if (is_long_mode(vcpu)) {

		save_msrs(vcpu->guest_msrs, NR_BAD_MSRS);

		load_msrs(vcpu->host_msrs, NR_BAD_MSRS);

	}

#endif

	save_msrs(vcpu->guest_msrs, vcpu->save_nmsrs);

	load_msrs(vcpu->host_msrs, vcpu->save_nmsrs);

}



/*
@@ -463,6 +456,20 @@ static void vmx_inject_gp(struct kvm_vcpu *vcpu, unsigned error_code) 
		     INTR_INFO_VALID_MASK);

}



/*

 * Swap MSR entry in host/guest MSR entry array.

 */

void move_msr_up(struct kvm_vcpu *vcpu, int from, int to)

{

	struct vmx_msr_entry tmp;

	tmp = vcpu->guest_msrs[to];

	vcpu->guest_msrs[to] = vcpu->guest_msrs[from];

	vcpu->guest_msrs[from] = tmp;

	tmp = vcpu->host_msrs[to];

	vcpu->host_msrs[to] = vcpu->host_msrs[from];

	vcpu->host_msrs[from] = tmp;

}



/*

 * Set up the vmcs to automatically save and restore system

 * msrs.  Don't touch the 64-bit msrs if the guest is in legacy
@@ -470,35 +477,54 @@ static void vmx_inject_gp(struct kvm_vcpu *vcpu, unsigned error_code) 
 */

static void setup_msrs(struct kvm_vcpu *vcpu)

{

	int nr_skip, nr_good_msrs;



	if (is_long_mode(vcpu))

		nr_skip = NR_BAD_MSRS;

	else

		nr_skip = NR_64BIT_MSRS;

	nr_good_msrs = vcpu->nmsrs - nr_skip;

	int index, save_nmsrs;



	save_nmsrs = 0;

#ifdef CONFIG_X86_64

	if (is_long_mode(vcpu)) {

		index = __find_msr_index(vcpu, MSR_SYSCALL_MASK);

		if (index >= 0)

			move_msr_up(vcpu, index, save_nmsrs++);

		index = __find_msr_index(vcpu, MSR_LSTAR);

		if (index >= 0)

			move_msr_up(vcpu, index, save_nmsrs++);

		index = __find_msr_index(vcpu, MSR_CSTAR);

		if (index >= 0)

			move_msr_up(vcpu, index, save_nmsrs++);

		index = __find_msr_index(vcpu, MSR_KERNEL_GS_BASE);

		if (index >= 0)

			move_msr_up(vcpu, index, save_nmsrs++);

		/*

		 * MSR_K6_STAR is only needed on long mode guests, and only

		 * if efer.sce is enabled.

		 */

	if (find_msr_entry(vcpu, MSR_K6_STAR)) {

		--nr_good_msrs;

		index = __find_msr_index(vcpu, MSR_K6_STAR);

		if ((index >= 0) && (vcpu->shadow_efer & EFER_SCE))

			move_msr_up(vcpu, index, save_nmsrs++);

	}

#endif

	vcpu->save_nmsrs = save_nmsrs;



#ifdef CONFIG_X86_64

		if (is_long_mode(vcpu) && (vcpu->shadow_efer & EFER_SCE))

			++nr_good_msrs;

	vcpu->msr_offset_kernel_gs_base =

		__find_msr_index(vcpu, MSR_KERNEL_GS_BASE);

#endif

	index = __find_msr_index(vcpu, MSR_EFER);

	if (index >= 0)

		save_nmsrs = 1;

	else {

		save_nmsrs = 0;

		index = 0;

	}



	vmcs_writel(VM_ENTRY_MSR_LOAD_ADDR,

		    virt_to_phys(vcpu->guest_msrs + nr_skip));

		    virt_to_phys(vcpu->guest_msrs + index));

	vmcs_writel(VM_EXIT_MSR_STORE_ADDR,

		    virt_to_phys(vcpu->guest_msrs + nr_skip));

		    virt_to_phys(vcpu->guest_msrs + index));

	vmcs_writel(VM_EXIT_MSR_LOAD_ADDR,

		    virt_to_phys(vcpu->host_msrs + nr_skip));

	vmcs_write32(VM_EXIT_MSR_STORE_COUNT, nr_good_msrs); /* 22.2.2 */

	vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, nr_good_msrs);  /* 22.2.2 */

	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, nr_good_msrs); /* 22.2.2 */

		    virt_to_phys(vcpu->host_msrs + index));

	vmcs_write32(VM_EXIT_MSR_STORE_COUNT, save_nmsrs);

	vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, save_nmsrs);

	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, save_nmsrs);

}



/*
@@ -595,14 +621,6 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data) 
	case MSR_GS_BASE:

		vmcs_writel(GUEST_GS_BASE, data);

		break;

	case MSR_LSTAR:

	case MSR_SYSCALL_MASK:

		msr = find_msr_entry(vcpu, msr_index);

		if (msr)

			msr->data = data;

		if (vcpu->vmx_host_state.loaded)

			load_msrs(vcpu->guest_msrs, NR_BAD_MSRS);

		break;

#endif

	case MSR_IA32_SYSENTER_CS:

		vmcs_write32(GUEST_SYSENTER_CS, data);
@@ -620,6 +638,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data) 
		msr = find_msr_entry(vcpu, msr_index);

		if (msr) {

			msr->data = data;

			if (vcpu->vmx_host_state.loaded)

				load_msrs(vcpu->guest_msrs,vcpu->save_nmsrs);

			break;

		}

		return kvm_set_msr_common(vcpu, msr_index, data);
@@ -1331,10 +1351,6 @@ static int vmx_vcpu_setup(struct kvm_vcpu *vcpu) 
		vcpu->host_msrs[j].reserved = 0;

		vcpu->host_msrs[j].data = data;

		vcpu->guest_msrs[j] = vcpu->host_msrs[j];

#ifdef CONFIG_X86_64

		if (index == MSR_KERNEL_GS_BASE)

			msr_offset_kernel_gs_base = j;

#endif

		++vcpu->nmsrs;

	}

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