Commit 4b8d54f9 authored by Zhai, Edwin's avatar Zhai, Edwin Committed by Avi Kivity
Browse files

KVM: VMX: Add support for Pause-Loop Exiting



New NHM processors will support Pause-Loop Exiting by adding 2 VM-execution
control fields:
PLE_Gap    - upper bound on the amount of time between two successive
             executions of PAUSE in a loop.
PLE_Window - upper bound on the amount of time a guest is allowed to execute in
             a PAUSE loop

If the time, between this execution of PAUSE and previous one, exceeds the
PLE_Gap, processor consider this PAUSE belongs to a new loop.
Otherwise, processor determins the the total execution time of this loop(since
1st PAUSE in this loop), and triggers a VM exit if total time exceeds the
PLE_Window.
* Refer SDM volume 3b section 21.6.13 & 22.1.3.

Pause-Loop Exiting can be used to detect Lock-Holder Preemption, where one VP
is sched-out after hold a spinlock, then other VPs for same lock are sched-in
to waste the CPU time.

Our tests indicate that most spinlocks are held for less than 212 cycles.
Performance tests show that with 2X LP over-commitment we can get +2% perf
improvement for kernel build(Even more perf gain with more LPs).
Signed-off-by: default avatarZhai Edwin <edwin.zhai@intel.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent d255f4f2
......@@ -56,6 +56,7 @@
#define SECONDARY_EXEC_ENABLE_VPID 0x00000020
#define SECONDARY_EXEC_WBINVD_EXITING 0x00000040
#define SECONDARY_EXEC_UNRESTRICTED_GUEST 0x00000080
#define SECONDARY_EXEC_PAUSE_LOOP_EXITING 0x00000400
#define PIN_BASED_EXT_INTR_MASK 0x00000001
......@@ -144,6 +145,8 @@ enum vmcs_field {
VM_ENTRY_INSTRUCTION_LEN = 0x0000401a,
TPR_THRESHOLD = 0x0000401c,
SECONDARY_VM_EXEC_CONTROL = 0x0000401e,
PLE_GAP = 0x00004020,
PLE_WINDOW = 0x00004022,
VM_INSTRUCTION_ERROR = 0x00004400,
VM_EXIT_REASON = 0x00004402,
VM_EXIT_INTR_INFO = 0x00004404,
......@@ -248,6 +251,7 @@ enum vmcs_field {
#define EXIT_REASON_MSR_READ 31
#define EXIT_REASON_MSR_WRITE 32
#define EXIT_REASON_MWAIT_INSTRUCTION 36
#define EXIT_REASON_PAUSE_INSTRUCTION 40
#define EXIT_REASON_MCE_DURING_VMENTRY 41
#define EXIT_REASON_TPR_BELOW_THRESHOLD 43
#define EXIT_REASON_APIC_ACCESS 44
......
......@@ -61,6 +61,25 @@ module_param_named(unrestricted_guest,
static int __read_mostly emulate_invalid_guest_state = 0;
module_param(emulate_invalid_guest_state, bool, S_IRUGO);
/*
* These 2 parameters are used to config the controls for Pause-Loop Exiting:
* ple_gap: upper bound on the amount of time between two successive
* executions of PAUSE in a loop. Also indicate if ple enabled.
* According to test, this time is usually small than 41 cycles.
* ple_window: upper bound on the amount of time a guest is allowed to execute
* in a PAUSE loop. Tests indicate that most spinlocks are held for
* less than 2^12 cycles
* Time is measured based on a counter that runs at the same rate as the TSC,
* refer SDM volume 3b section 21.6.13 & 22.1.3.
*/
#define KVM_VMX_DEFAULT_PLE_GAP 41
#define KVM_VMX_DEFAULT_PLE_WINDOW 4096
static int ple_gap = KVM_VMX_DEFAULT_PLE_GAP;
module_param(ple_gap, int, S_IRUGO);
static int ple_window = KVM_VMX_DEFAULT_PLE_WINDOW;
module_param(ple_window, int, S_IRUGO);
struct vmcs {
u32 revision_id;
u32 abort;
......@@ -319,6 +338,12 @@ static inline int cpu_has_vmx_unrestricted_guest(void)
SECONDARY_EXEC_UNRESTRICTED_GUEST;
}
static inline int cpu_has_vmx_ple(void)
{
return vmcs_config.cpu_based_2nd_exec_ctrl &
SECONDARY_EXEC_PAUSE_LOOP_EXITING;
}
static inline int vm_need_virtualize_apic_accesses(struct kvm *kvm)
{
return flexpriority_enabled &&
......@@ -1240,7 +1265,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
SECONDARY_EXEC_WBINVD_EXITING |
SECONDARY_EXEC_ENABLE_VPID |
SECONDARY_EXEC_ENABLE_EPT |
SECONDARY_EXEC_UNRESTRICTED_GUEST;
SECONDARY_EXEC_UNRESTRICTED_GUEST |
SECONDARY_EXEC_PAUSE_LOOP_EXITING;
if (adjust_vmx_controls(min2, opt2,
MSR_IA32_VMX_PROCBASED_CTLS2,
&_cpu_based_2nd_exec_control) < 0)
......@@ -1386,6 +1412,9 @@ static __init int hardware_setup(void)
if (enable_ept && !cpu_has_vmx_ept_2m_page())
kvm_disable_largepages();
if (!cpu_has_vmx_ple())
ple_gap = 0;
return alloc_kvm_area();
}
......@@ -2298,9 +2327,16 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
exec_control &= ~SECONDARY_EXEC_ENABLE_EPT;
if (!enable_unrestricted_guest)
exec_control &= ~SECONDARY_EXEC_UNRESTRICTED_GUEST;
if (!ple_gap)
exec_control &= ~SECONDARY_EXEC_PAUSE_LOOP_EXITING;
vmcs_write32(SECONDARY_VM_EXEC_CONTROL, exec_control);
}
if (ple_gap) {
vmcs_write32(PLE_GAP, ple_gap);
vmcs_write32(PLE_WINDOW, ple_window);
}
vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, !!bypass_guest_pf);
vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, !!bypass_guest_pf);
vmcs_write32(CR3_TARGET_COUNT, 0); /* 22.2.1 */
......@@ -3347,6 +3383,18 @@ out:
return ret;
}
/*
* Indicate a busy-waiting vcpu in spinlock. We do not enable the PAUSE
* exiting, so only get here on cpu with PAUSE-Loop-Exiting.
*/
static int handle_pause(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
{
skip_emulated_instruction(vcpu);
kvm_vcpu_on_spin(vcpu);
return 1;
}
/*
* The exit handlers return 1 if the exit was handled fully and guest execution
* may resume. Otherwise they set the kvm_run parameter to indicate what needs
......@@ -3383,6 +3431,7 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[EXIT_REASON_MCE_DURING_VMENTRY] = handle_machine_check,
[EXIT_REASON_EPT_VIOLATION] = handle_ept_violation,
[EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
[EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
};
static const int kvm_vmx_max_exit_handlers =
......
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