[PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v2)

Anthony Liguori
2010-12-02T13:59:24Z

In certain use-cases, we want to allocate guests fixed time slices where idle
guest cycles leave the machine idling. There are many approaches to achieve
this but the most direct is to simply avoid trapping the HLT instruction which
lets the guest directly execute the instruction putting the processor to sleep.

Introduce this as a module-level option for kvm-vmx.ko since if you do this
for one guest, you probably want to do it for all. A similar option is possible
for AMD but I don't have easy access to AMD test hardware.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
---
v1 -> v2
- Rename parameter to yield_on_hlt
- Remove __read_mostly

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index caa967e..d8310e4 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -69,6 +69,9 @@ module_param(emulate_invalid_guest_state, bool, S_IRUGO);
static int __read_mostly vmm_exclusive = 1;
module_param(vmm_exclusive, bool, S_IRUGO);

+static int yield_on_hlt = 1;
+module_param(yield_on_hlt, bool, S_IRUGO);
+
#define KVM_GUEST_CR0_MASK_UNRESTRICTED_GUEST \
(X86_CR0_WP | X86_CR0_NE | X86_CR0_NW | X86_CR0_CD)
#define KVM_GUEST_CR0_MASK \
@@ -1419,7 +1422,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
&_pin_based_exec_control) < 0)
return -EIO;

- min = CPU_BASED_HLT_EXITING |
+ min =
#ifdef CONFIG_X86_64
CPU_BASED_CR8_LOAD_EXITING |
CPU_BASED_CR8_STORE_EXITING |
@@ -1432,6 +1435,10 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
CPU_BASED_MWAIT_EXITING |
CPU_BASED_MONITOR_EXITING |
CPU_BASED_INVLPG_EXITING;
+
+ if (yield_on_hlt)
+ min |= CPU_BASED_HLT_EXITING;
+
opt = CPU_BASED_TPR_SHADOW |
CPU_BASED_USE_MSR_BITMAPS |
CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
--
1.7.0.4