On 2013-08-25 09:24, Arthur Chunqi Li wrote:
> 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.
Sorry, parsed the code incorrectly.
> 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.
Yes. The point is that we will not even expose
PIN_BASED_VMX_PREEMPTION_TIMER if VM_EXIT_SAVE_VMX_PREEMPTION_TIMER is
missing. If the guest then requests the former, it simply sets an
invalid pin-based control value which we already catch and report. So
this hunk becomes redundant.
Jan
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