On Sun, Aug 25, 2013 at 2:44 PM, Jan Kiszka <jan.kiszka@xxxxxx> wrote:
> On 2013-08-24 20:44, root 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 <yzt356@xxxxxxxxx>
>> ---
>> arch/x86/kvm/vmx.c | 30 +++++++++++++++++++++++++-----
>> 1 file changed, 25 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 57b4e12..9579409 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2204,7 +2204,8 @@ 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;
>> nested_vmx_exit_ctls_high |= (VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
>> VM_EXIT_LOAD_IA32_EFER);
>
> In the absence of VM_EXIT_SAVE_VMX_PREEMPTION_TIMER, you need to hide
> PIN_BASED_VMX_PREEMPTION_TIMER from the guest as we cannot emulate its
> behavior properly in that case.
>
>>
>> @@ -7578,9 +7579,14 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>> (vmcs_config.pin_based_exec_ctrl |
>> vmcs12->pin_based_vm_exec_control));
>>
>> - if (vmcs12->pin_based_vm_exec_control & PIN_BASED_VMX_PREEMPTION_TIMER)
>> - vmcs_write32(VMX_PREEMPTION_TIMER_VALUE,
>> - vmcs12->vmx_preemption_timer_value);
>> + 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);
>> + }
>
> This is not correct. We still need to set the vmcs to
> vmx_preemption_timer_value. The difference is that, on exit from L2,
> vmx_preemption_timer_value has to be updated according to the saved
> hardware state. The corresponding code is missing in your patch so far.
>
>>
>> /*
>> * Whether page-faults are trapped is determined by a combination of
>> @@ -7690,7 +7696,11 @@ 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);
>> + if (vmcs12->pin_based_vm_exec_control & PIN_BASED_VMX_PREEMPTION_TIMER)
>> + vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl |
>> + VM_EXIT_SAVE_VMX_PREEMPTION_TIMER);
>> + else
>> + vmcs_write32(VM_EXIT_CONTROLS, vmcs_config.vmexit_ctrl);
>
> Let's prepare the value for VM_EXIT_CONTROLS in a local variable first,
> then write it to the vmcs.
>
>>
>> /* vmcs12's VM_ENTRY_LOAD_IA32_EFER and VM_ENTRY_IA32E_MODE are
>> * emulated by vmx_set_efer(), below.
>> @@ -7912,6 +7922,16 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>> }
>>
>> /*
>> + * If L2 support PIN_BASED_VMX_PREEMPTION_TIMER, L0 must support
>> + * VM_EXIT_SAVE_VMX_PREEMPTION_TIMER.
>> + */
>> + if ((vmcs12->pin_based_vm_exec_control & PIN_BASED_VMX_PREEMPTION_TIMER) &&
>> + !(nested_vmx_exit_ctls_high & VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)) {
>> + nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
>> + return 1;
>> + }
>
> Nope, the guest is free to run the preemption timer without saving on
> exits. It may have a valid use case for this, e.g. that it will always
> reprogram it on entry.
Here "!(nested_vmx_exit_ctls_high &
VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)" is used to detect if hardware
support "save preemption timer" feature, which means if L2 supports
pinbased vmx preemption timer, host must support "save preemption
timer" feature. Though nested_vmx_exit_ctls_* is used for nested env,
but it can also used to reflect the host's feature. Here is what I
discuss with you yesterday, and we can also get the feature via
"rdmsr" here to avoid the confusion.
Arthur
>
>> +
>> + /*
>> * We're finally done with prerequisite checking, and can start with
>> * the nested entry.
>> */
>>
>
> Jan
>
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