2017-06-16 23:38 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>:
> 2017-06-16 22:24+0800, Wanpeng Li:
>> 2017-06-16 21:37 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>:
>> > 2017-06-14 19:26-0700, Wanpeng Li:
>> >> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>> >>
>> >> Add an async_page_fault field to vcpu->arch.exception to identify an async
>> >> page fault, and constructs the expected vm-exit information fields. Force
>> >> a nested VM exit from nested_vmx_check_exception() if the injected #PF
>> >> is async page fault.
>> >>
>> >> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> >> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
>> >> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>> >> ---
>> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> >> @@ -452,7 +452,11 @@ EXPORT_SYMBOL_GPL(kvm_complete_insn_gp);
>> >> void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault)
>> >> {
>> >> ++vcpu->stat.pf_guest;
>> >> - vcpu->arch.cr2 = fault->address;
>> >> + vcpu->arch.exception.async_page_fault = fault->async_page_fault;
>> >
>> > I think we need to act as if arch.exception.async_page_fault was not
>> > pending in kvm_vcpu_ioctl_x86_get_vcpu_events(). Otherwise, if we
>> > migrate with pending async_page_fault exception, we'd inject it as a
>> > normal #PF, which could confuse/kill the nested guest.
>> >
>> > And kvm_vcpu_ioctl_x86_set_vcpu_events() should clean the flag for
>> > sanity as well.
>>
>> Do you mean we should add a field like async_page_fault to
>> kvm_vcpu_events::exception, then saves arch.exception.async_page_fault
>> to events->exception.async_page_fault through KVM_GET_VCPU_EVENTS and
>> restores events->exception.async_page_fault to
>> arch.exception.async_page_fault through KVM_SET_VCPU_EVENTS?
>
> No, I thought we could get away with a disgusting hack of hiding the
> exception from userspace, which would work for migration, but not if
> local userspace did KVM_GET_VCPU_EVENTS and KVM_SET_VCPU_EVENTS ...
>
> Extending the userspace interface would work, but I'd do it as a last
> resort, after all conservative solutions have failed.
> async_pf migration is very crude, so exposing the exception is just an
> ugly workaround for the local case. Adding the flag would also require
> userspace configuration of async_pf features for the guest to keep
> compatibility.
>
> I see two options that might be simpler than adding the userspace flag:
>
> 1) do the nested VM exit sooner, at the place where we now queue #PF,
> 2) queue the #PF later, save the async_pf in some intermediate
> structure and consume it at the place where you proposed the nested
> VM exit.
How about something like this to not get exception events if it is
"is_guest_mode(vcpu) && vcpu->arch.exception.nr == PF_VECTOR &&
vcpu->arch.exception.async_page_fault" since lost a reschedule
optimization is not that importmant in L1.
@@ -3072,13 +3074,16 @@ static void
kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
struct kvm_vcpu_events *events)
{
process_nmi(vcpu);
- events->exception.injected =
- vcpu->arch.exception.pending &&
- !kvm_exception_is_soft(vcpu->arch.exception.nr);
- events->exception.nr = vcpu->arch.exception.nr;
- events->exception.has_error_code = vcpu->arch.exception.has_error_code;
- events->exception.pad = 0;
- events->exception.error_code = vcpu->arch.exception.error_code;
+ if (!(is_guest_mode(vcpu) && vcpu->arch.exception.nr == PF_VECTOR &&
+ vcpu->arch.exception.async_page_fault)) {
+ events->exception.injected =
+ vcpu->arch.exception.pending &&
+ !kvm_exception_is_soft(vcpu->arch.exception.nr);
+ events->exception.nr = vcpu->arch.exception.nr;
+ events->exception.has_error_code = vcpu->arch.exception.has_error_code;
+ events->exception.pad = 0;
+ events->exception.error_code = vcpu->arch.exception.error_code;
+ }
Regards,
Wanpeng Li
