Commit 94dfbdb3 authored by Anthony Liguori's avatar Anthony Liguori Committed by Avi Kivity
Browse files

KVM: SVM: Only save/restore MSRs when needed 



We only have to save/restore MSR_GS_BASE on every VMEXIT.  The rest can be
saved/restored when we leave the VCPU.  Since we don't emulate the DEBUGCTL
MSRs and the guest cannot write to them, we don't have to worry about
saving/restoring them at all.

This shaves a whopping 40% off raw vmexit costs on AMD.

Signed-off-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent 2807696c

drivers/kvm/kvm_svm.h

+5 −6
Original line number Diff line number Diff line
@@ -9,17 +9,15 @@ 
#include "svm.h"

#include "kvm.h"



static const u32 host_save_msrs[] = {

static const u32 host_save_user_msrs[] = {

#ifdef CONFIG_X86_64

	MSR_STAR, MSR_LSTAR, MSR_CSTAR, MSR_SYSCALL_MASK, MSR_KERNEL_GS_BASE,

	MSR_FS_BASE, MSR_GS_BASE,

	MSR_FS_BASE,

#endif

	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,

	MSR_IA32_DEBUGCTLMSR, /*MSR_IA32_LASTBRANCHFROMIP,

	MSR_IA32_LASTBRANCHTOIP, MSR_IA32_LASTINTFROMIP,MSR_IA32_LASTINTTOIP,*/

};



#define NR_HOST_SAVE_MSRS ARRAY_SIZE(host_save_msrs)

#define NR_HOST_SAVE_USER_MSRS ARRAY_SIZE(host_save_user_msrs)

#define NUM_DB_REGS 4



struct vcpu_svm {
@@ -32,7 +30,8 @@ struct vcpu_svm { 


	u64 next_rip;



	u64 host_msrs[NR_HOST_SAVE_MSRS];

	u64 host_user_msrs[NR_HOST_SAVE_USER_MSRS];

	u64 host_gs_base;

	unsigned long host_cr2;

	unsigned long host_db_regs[NUM_DB_REGS];

	unsigned long host_dr6;

drivers/kvm/svm.c

+15 −11
Original line number Diff line number Diff line
@@ -522,8 +522,6 @@ static void init_vmcb(struct vmcb *vmcb) 
	control->msrpm_base_pa = msrpm_base;

	control->tsc_offset = 0;

	control->int_ctl = V_INTR_MASKING_MASK;

	if (svm_has(SVM_FEATURE_LBRV))

		control->lbr_ctl = 1ULL;



	init_seg(&save->es);

	init_seg(&save->ss);
@@ -611,7 +609,7 @@ static void svm_free_vcpu(struct kvm_vcpu *vcpu) 


static void svm_vcpu_load(struct kvm_vcpu *vcpu)

{

	int cpu;

	int cpu, i;



	cpu = get_cpu();

	if (unlikely(cpu != vcpu->cpu)) {
@@ -626,10 +624,18 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu) 
		vcpu->svm->vmcb->control.tsc_offset += delta;

		vcpu->cpu = cpu;

	}



	for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)

		rdmsrl(host_save_user_msrs[i], vcpu->svm->host_user_msrs[i]);

}



static void svm_vcpu_put(struct kvm_vcpu *vcpu)

{

	int i;



	for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)

		wrmsrl(host_save_user_msrs[i], vcpu->svm->host_user_msrs[i]);



	rdtscll(vcpu->host_tsc);

	put_cpu();

}
@@ -815,18 +821,16 @@ static int svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_debug_guest *dbg) 


static void load_host_msrs(struct kvm_vcpu *vcpu)

{

	int i;



	for ( i = 0; i < NR_HOST_SAVE_MSRS; i++)

		wrmsrl(host_save_msrs[i], vcpu->svm->host_msrs[i]);

#ifdef CONFIG_X86_64

	wrmsrl(MSR_GS_BASE, vcpu->svm->host_gs_base);

#endif

}



static void save_host_msrs(struct kvm_vcpu *vcpu)

{

	int i;



	for ( i = 0; i < NR_HOST_SAVE_MSRS; i++)

		rdmsrl(host_save_msrs[i], vcpu->svm->host_msrs[i]);

#ifdef CONFIG_X86_64

	rdmsrl(MSR_GS_BASE, vcpu->svm->host_gs_base);

#endif

}



static void new_asid(struct kvm_vcpu *vcpu, struct svm_cpu_data *svm_data)

CRA Git | Maintained and supported by SUSTech CRA and CCSE