Re: [PATCH] KVM: nVMX: Fully support of nested VMX preemption timer

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-08-25 09:37, Arthur Chunqi Li wrote:
> On Sun, Aug 25, 2013 at 3:28 PM, Jan Kiszka <jan.kiszka@web.de> wrote:
>> On 2013-08-25 09:24, Arthur Chunqi Li wrote:
>>> On Sun, Aug 25, 2013 at 2:44 PM, Jan Kiszka <jan.kiszka@web.de> 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@gmail.com>
>>>>> ---
>>>>>  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.
> Besides, we need to test that in the absence of
> PIN_BASED_VMX_PREEMPTION_TIMER, we need to hide
> VM_EXIT_SAVE_VMX_PREEMPTION_TIMER, though this should not happen
> according to Intel SDM.

If the SDM guarantees this for us, we don't need such a safety measure.
Otherwise, it should be added, yes.

Jan



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