On Mon, Aug 26, 2013 at 3:23 PM, Jan Kiszka <[email protected]> wrote:
> On 2013-08-25 17:26, Arthur Chunqi Li wrote:
>> This patch contains the following two changes:
>> 1. Fix the bug in nested preemption timer support. If vmexit L2->L0
>> with some reasons not emulated by L1, preemption timer value should
>> be save in such exits.
>> 2. Add support of "Save VMX-preemption timer value" VM-Exit controls
>> to nVMX.
>>
>> With this patch, nested VMX preemption timer features are fully
>> supported.
>>
>> Signed-off-by: Arthur Chunqi Li <[email protected]>
>> ---
>> arch/x86/kvm/vmx.c | 49 ++++++++++++++++++++++++++++++++++++++++++++-----
>> 1 file changed, 44 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 57b4e12..6aa320e 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2204,7 +2204,14 @@ static __init void nested_vmx_setup_ctls_msrs(void)
>> #ifdef CONFIG_X86_64
>> VM_EXIT_HOST_ADDR_SPACE_SIZE |
>> #endif
>> - VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT;
>> + VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT |
>> + VM_EXIT_SAVE_VMX_PREEMPTION_TIMER;
>> + if (!(nested_vmx_pinbased_ctls_high & PIN_BASED_VMX_PREEMPTION_TIMER))
>> + nested_vmx_exit_ctls_high &=
>> + (~VM_EXIT_SAVE_VMX_PREEMPTION_TIMER);
>> + if (!(nested_vmx_exit_ctls_high & VM_EXIT_SAVE_VMX_PREEMPTION_TIMER))
>> + nested_vmx_pinbased_ctls_high &=
>> + (~PIN_BASED_VMX_PREEMPTION_TIMER);
>> nested_vmx_exit_ctls_high |= (VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
>> VM_EXIT_LOAD_IA32_EFER);
>>
>> @@ -6706,6 +6713,22 @@ static void vmx_get_exit_info(struct kvm_vcpu *vcpu,
>> u64 *info1, u64 *info2)
>> *info2 = vmcs_read32(VM_EXIT_INTR_INFO);
>> }
>>
>> +static void nested_fix_preempt(struct kvm_vcpu *vcpu)
>
> nested_adjust_preemption_timer - just "preempt" can be misleading.
>
>> +{
>> + u64 delta_guest_tsc;
>> + u32 preempt_val, preempt_bit, delta_preempt_val;
>> +
>> + preempt_bit = native_read_msr(MSR_IA32_VMX_MISC) & 0x1F;
>
> This is rather preemption_timer_scale. And if there is no symbolic value
> for the bitmask, please introduce one.
>
>> + delta_guest_tsc = kvm_x86_ops->read_l1_tsc(vcpu,
>> + native_read_tsc()) - vcpu->arch.last_guest_tsc;
>> + delta_preempt_val = delta_guest_tsc >> preempt_bit;
>> + preempt_val = vmcs_read32(VMX_PREEMPTION_TIMER_VALUE);
>> + if (preempt_val - delta_preempt_val < 0)
>> + preempt_val = 0;
>> + else
>> + preempt_val -= delta_preempt_val;
>> + vmcs_write32(VMX_PREEMPTION_TIMER_VALUE, preempt_val);
>
> The rest unfortunately wrong. It has to be split into two parts: Part
> one, the calculation of L1's TSC value and its storing in nested_vmx,
> has to be done on vmexit. Part two, reading the current TSC, calculating
> the time spent in L0 and converting it into L1 TSC time, this has to be
> done right before vmentry of L2.
As what we discussed yesterday, the calculation of L1's TSC value is
not saved in nested_vmx, however, to avoid adding codes to the hot
patch of vmexit. Instead, we use vcpu->arch.last_guest_tsc as the
value stored on vmexit (which has been done already). And the value of
"part two" is calculated in nested_fix_preempt() above (see variant
delta_guest_tsc, which stores the consumed TSC value in L0). Since
vmx_handle_exit is the last function called in vmexit path, I think
it's OK to put "part two" here.
>
> Arthur, please make sure that your test case detects the current
> breakage of preemption timer emulation properly, both /wrt to missing
> save/restore and also regarding missing L0 time compensation, and then
> check that your KVM patch fixes it based on the unit test results.
OK, I will commit a patch of kvm-unit-tests to test these changes.
Arthur
>
> Jan
>
>> +}
>> /*
>> * The guest has exited. See if we can fix it or if we need userspace
>> * assistance.
>> @@ -6734,9 +6757,12 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
>> else
>> vmx->nested.nested_run_pending = 0;
>>
>> - if (is_guest_mode(vcpu) && nested_vmx_exit_handled(vcpu)) {
>> - nested_vmx_vmexit(vcpu);
>> - return 1;
>> + if (is_guest_mode(vcpu)) {
>> + if (nested_vmx_exit_handled(vcpu)) {
>> + nested_vmx_vmexit(vcpu);
>> + return 1;
>> + } else
>> + nested_fix_preempt(vcpu);
>> }
>>
>> if (exit_reason & VMX_EXIT_REASONS_FAILED_VMENTRY) {
>> @@ -7517,6 +7543,7 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu,
>> struct vmcs12 *vmcs12)
>> {
>> struct vcpu_vmx *vmx = to_vmx(vcpu);
>> u32 exec_control;
>> + u32 exit_control;
>>
>> vmcs_write16(GUEST_ES_SELECTOR, vmcs12->guest_es_selector);
>> vmcs_write16(GUEST_CS_SELECTOR, vmcs12->guest_cs_selector);
>> @@ -7690,7 +7717,10 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu,
>> struct vmcs12 *vmcs12)
>> * we should use its exit controls. Note that VM_EXIT_LOAD_IA32_EFER
>> * bits are further modified by vmx_set_efer() below.
>> */
>> - vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl);
>> + exit_control = vmcs_config.vmexit_ctrl;
>> + if (vmcs12->pin_based_vm_exec_control & PIN_BASED_VMX_PREEMPTION_TIMER)
>> + exit_control |= VM_EXIT_SAVE_VMX_PREEMPTION_TIMER;
>> + vmcs_write32(VM_EXIT_CONTROLS, exit_control);
>>
>> /* vmcs12's VM_ENTRY_LOAD_IA32_EFER and VM_ENTRY_IA32E_MODE are
>> * emulated by vmx_set_efer(), below.
>> @@ -8089,6 +8119,15 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu,
>> struct vmcs12 *vmcs12)
>> vmcs12->guest_pending_dbg_exceptions =
>> vmcs_readl(GUEST_PENDING_DBG_EXCEPTIONS);
>>
>> + if (vmcs12->pin_based_vm_exec_control &
>> PIN_BASED_VMX_PREEMPTION_TIMER) {
>> + if (vmcs12->vm_exit_controls &
>> VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)
>> + vmcs12->vmx_preemption_timer_value =
>> + vmcs_read32(VMX_PREEMPTION_TIMER_VALUE);
>> + else
>> + vmcs_write32(VMX_PREEMPTION_TIMER_VALUE,
>> + vmcs12->vmx_preemption_timer_value);
>> + }
>> +
>> /*
>> * In some cases (usually, nested EPT), L2 is allowed to change its
>> * own CR3 without exiting. If it has changed it, we must keep it.
>>
>
>
--
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China
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