On 9/6/2023 2:24 PM, Hao Peng wrote:
From: Peng Hao <flyingpeng@xxxxxxxxxxx>
The call of vcpu_load/put takes about 1-2us. Each
kvm_arch_vcpu_create will call vcpu_load/put
to initialize some fields of vmcs, which can be
delayed until the call of vcpu_ioctl to process
this part of the vmcs field, which can reduce calls
to vcpu_load.
what if no vcpu ioctl is called after vcpu creation?
And will the first (it was second before this patch) vcpu_load() becomes
longer? have you measured it?
I don't think it worth the optimization unless a strong reason.
Signed-off-by: Peng Hao <flyingpeng@xxxxxxxxxxx>
---
arch/x86/include/asm/kvm_host.h | 1 +
arch/x86/kvm/x86.c | 21 ++++++++++++++++-----
2 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 9320019708f9..2f2dcd283788 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -984,6 +984,7 @@ struct kvm_vcpu_arch {
/* Flush the L1 Data cache for L1TF mitigation on VMENTER */
bool l1tf_flush_l1d;
+ bool initialized;
/* Host CPU on which VM-entry was most recently attempted */
int last_vmentry_cpu;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4fd08a5e0e98..a3671a54e850 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -317,7 +317,20 @@ const struct kvm_stats_header kvm_vcpu_stats_header = {
u64 __read_mostly host_xcr0;
static struct kmem_cache *x86_emulator_cache;
+static int kvm_set_tsc_khz(struct kvm_vcpu *vcpu, u32 user_tsc_khz);
+static inline bool kvm_vcpu_initialized(struct kvm_vcpu *vcpu)
+{
+ return vcpu->arch.initialized;
+}
+
+static void kvm_vcpu_initial_reset(struct kvm_vcpu *vcpu)
+{
+ kvm_set_tsc_khz(vcpu, vcpu->kvm->arch.default_tsc_khz);
+ kvm_vcpu_reset(vcpu, false);
+ kvm_init_mmu(vcpu);
+ vcpu->arch.initialized = true;
+}
/*
* When called, it means the previous get/set msr reached an invalid msr.
* Return true if we want to ignore/silent this failed msr access.
@@ -5647,6 +5660,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
vcpu_load(vcpu);
+ if (!kvm_vcpu_initialized(vcpu))
+ kvm_vcpu_initial_reset(vcpu);
+
u.buffer = NULL;
switch (ioctl) {
case KVM_GET_LAPIC: {
@@ -11930,11 +11946,6 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
kvm_xen_init_vcpu(vcpu);
kvm_vcpu_mtrr_init(vcpu);
- vcpu_load(vcpu);
- kvm_set_tsc_khz(vcpu, vcpu->kvm->arch.default_tsc_khz);
- kvm_vcpu_reset(vcpu, false);
- kvm_init_mmu(vcpu);
- vcpu_put(vcpu);
return 0;
free_guest_fpu:
--
2.31.1
