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KVM: VMX: Explicitly initialize controls shadow at VMCS allocation 

Or: Don't re-initialize vmcs02's controls on every nested VM-Entry.

VMWRITEs to the major VMCS controls are deceptively expensive.  Intel
CPUs with VMCS caching (Westmere and later) also optimize away
consistency checks on VM-Entry, i.e. skip consistency checks if the
relevant fields have not changed since the last successful VM-Entry (of
the cached VMCS).  Because uops are a precious commodity, uCode's dirty
VMCS field tracking isn't as precise as software would prefer.  Notably,
writing any of the major VMCS fields effectively marks the entire VMCS
dirty, i.e. causes the next VM-Entry to perform all consistency checks,
which consumes several hundred cycles.

Zero out the controls' shadow copies during VMCS allocation and use the
optimized setter when "initializing" controls.  While this technically
affects both non-nested and nested virtualization, nested virtualization
is the primary beneficiary as avoid VMWRITEs when prepare vmcs02 allows
hardware to optimizie away consistency checks.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
alistair/sunxi64-5.4-dsi
Sean Christopherson 2019-05-07 12:18:00 -07:00 committed by Paolo Bonzini
parent ae81d08993
commit 3af80fec6e
3 changed files with 12 additions and 15 deletions
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10
arch/x86/kvm/vmx/nested.c
View File

@ -2024,7 +2024,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
} else {
exec_control &= ~PIN_BASED_POSTED_INTR;
}
pin_controls_init(vmx, exec_control);
pin_controls_set(vmx, exec_control);
/*
* EXEC CONTROLS
@ -2049,7 +2049,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
*/
exec_control &= ~CPU_BASED_USE_IO_BITMAPS;
exec_control |= CPU_BASED_UNCOND_IO_EXITING;
exec_controls_init(vmx, exec_control);
exec_controls_set(vmx, exec_control);
/*
* SECONDARY EXEC CONTROLS
@ -2079,7 +2079,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
vmcs_write16(GUEST_INTR_STATUS,
vmcs12->guest_intr_status);
secondary_exec_controls_init(vmx, exec_control);
secondary_exec_controls_set(vmx, exec_control);
}
/*
@ -2098,7 +2098,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
if (guest_efer != host_efer)
exec_control |= VM_ENTRY_LOAD_IA32_EFER;
}
vm_entry_controls_init(vmx, exec_control);
vm_entry_controls_set(vmx, exec_control);
/*
* EXIT CONTROLS
@ -2110,7 +2110,7 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
exec_control = vmx_vmexit_ctrl();
if (cpu_has_load_ia32_efer() && guest_efer != host_efer)
exec_control |= VM_EXIT_LOAD_IA32_EFER;
vm_exit_controls_init(vmx, exec_control);
vm_exit_controls_set(vmx, exec_control);
/*
* Interrupt/Exception Fields

12
arch/x86/kvm/vmx/vmx.c
View File

@ -2485,6 +2485,8 @@ int alloc_loaded_vmcs(struct loaded_vmcs *loaded_vmcs)
}
memset(&loaded_vmcs->host_state, 0, sizeof(struct vmcs_host_state));
memset(&loaded_vmcs->controls_shadow, 0,
sizeof(struct vmcs_controls_shadow));
return 0;
@ -4040,14 +4042,14 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
vmcs_write64(VMCS_LINK_POINTER, -1ull); /* 22.3.1.5 */
/* Control */
pin_controls_init(vmx, vmx_pin_based_exec_ctrl(vmx));
pin_controls_set(vmx, vmx_pin_based_exec_ctrl(vmx));
vmx->hv_deadline_tsc = -1;
exec_controls_init(vmx, vmx_exec_control(vmx));
exec_controls_set(vmx, vmx_exec_control(vmx));
if (cpu_has_secondary_exec_ctrls()) {
vmx_compute_secondary_exec_control(vmx);
secondary_exec_controls_init(vmx, vmx->secondary_exec_control);
secondary_exec_controls_set(vmx, vmx->secondary_exec_control);
}
if (kvm_vcpu_apicv_active(&vmx->vcpu)) {
@ -4105,10 +4107,10 @@ static void vmx_vcpu_setup(struct vcpu_vmx *vmx)
++vmx->nmsrs;
}
vm_exit_controls_init(vmx, vmx_vmexit_ctrl());
vm_exit_controls_set(vmx, vmx_vmexit_ctrl());
/* 22.2.1, 20.8.1 */
vm_entry_controls_init(vmx, vmx_vmentry_ctrl());
vm_entry_controls_set(vmx, vmx_vmentry_ctrl());
vmx->vcpu.arch.cr0_guest_owned_bits = X86_CR0_TS;
vmcs_writel(CR0_GUEST_HOST_MASK, ~X86_CR0_TS);

5
arch/x86/kvm/vmx/vmx.h
View File

@ -388,11 +388,6 @@ static inline u8 vmx_get_rvi(void)
}
#define BUILD_CONTROLS_SHADOW(lname, uname) \
static inline void lname##_controls_init(struct vcpu_vmx *vmx, u32 val) \
{ \
vmcs_write32(uname, val); \
vmx->loaded_vmcs->controls_shadow.lname = val; \
} \
static inline void lname##_controls_set(struct vcpu_vmx *vmx, u32 val) \
{ \
if (vmx->loaded_vmcs->controls_shadow.lname != val) { \