Gleb Natapov wrote:
> On Fri, Apr 17, 2009 at 09:55:45PM +0200, Jan Kiszka wrote:
>> Gleb Natapov wrote:
>>> Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
>>> ---
>>> arch/x86/include/asm/kvm_host.h | 1 +
>>> arch/x86/kvm/svm.c | 49 +++++++++++++++++++++++++++++++++++++-
>>> 2 files changed, 48 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>>> index 8b6f6e9..057a612 100644
>>> --- a/arch/x86/include/asm/kvm_host.h
>>> +++ b/arch/x86/include/asm/kvm_host.h
>>> @@ -766,6 +766,7 @@ enum {
>>> #define HF_GIF_MASK (1 << 0)
>>> #define HF_HIF_MASK (1 << 1)
>>> #define HF_VINTR_MASK (1 << 2)
>>> +#define HF_NMI_MASK (1 << 3)
>>>
>>> /*
>>> * Hardware virtualization extension instructions may fault if a
>>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>>> index c605477..cd60fd7 100644
>>> --- a/arch/x86/kvm/svm.c
>>> +++ b/arch/x86/kvm/svm.c
>>> @@ -1834,6 +1834,13 @@ static int cpuid_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
>>> return 1;
>>> }
>>>
>>> +static int iret_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
>>> +{
>>> + svm->vmcb->control.intercept &= ~(1UL << INTERCEPT_IRET);
>>> + svm->vcpu.arch.hflags &= ~HF_NMI_MASK;
>>> + return 0;
>>> +}
>> First, this must return 1 (or set an exit reason, but there is no reason
>> to escape to user space here). And second, I think a corner case is not
>> handled the same way as on real iron: If there is already the next NMI
>> waiting, we will inject it before iret, not after its execution as it
>> should be.
>>
>> No easy solution for this yet. Maybe emulating iret, but there is no
>> implementation, specifically for protected mode. Maybe setting a
>> breakpoint. Or maybe enforcing a single step exception. Nothing trivial
>> in this list. On the other hand, this may only be a slight imprecision
>> of the virtualization. Need to think about it.
>>
> What about this:
> Instead of clearing HF_NMI_MASK in iret_interception() we can set
> another flag (HF_IRET) and on guest entry clear HF_NMI_MASK (and
> HF_IRET) if HF_IRET is set, but do that after checking for NMI
> injection. The pending NMI will be injected on the next entry.
> Also not how real HW works, but may be better then current situation.
It's OK as a first step towards correct NMI emulation. Additionally, you
could enable the IRQ window interception in case the is an NMI pending.
The resulting behavior should then much like the VNMI mask emulation for
vmx.
The next step should then be setting TF in the eflags stored on the
guest's stack before returning *if* there is already the next NMI
pending. But I wonder how much additional effort this will actually mean
(compared to the band-aid work)... :)
Jan
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