Re: [PATCH 3/4] KVM: async_pf: Force a nested vmexit if the injected #PF is async_pf

Radim Krčmář
2017-06-13T18:55:23Z

2017-06-12 23:08-0700, Wanpeng Li:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> 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@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> @@ -2422,13 +2422,28 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
> static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned nr)

This function could use the same treatment as vmx_queue_exception(), so
we are not mixing 'nr' with 'vcpu->arch.exception.*'.

> {
> struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> + u32 intr_info = 0;
> + unsigned long exit_qualification = 0;
>
> - if (!(vmcs12->exception_bitmap & (1u << nr)))
> + if (!((vmcs12->exception_bitmap & (1u << nr)) ||
> + (nr == PF_VECTOR && vcpu->arch.exception.async_page_fault)))
> return 0;
>
> + intr_info = nr | INTR_INFO_VALID_MASK;
> + exit_qualification = vmcs_readl(EXIT_QUALIFICATION);

This part still uses EXIT_QUALIFICATION(), which means it is not general
and I think it would be nicer to just do simple special case on top:

if (vcpu->arch.exception.async_page_fault) {
vmcs_write32(VM_EXIT_INTR_ERROR_CODE, vcpu->arch.exception.error_code);
nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI,
PF_VECTOR | INTR_TYPE_HARD_EXCEPTION |
INTR_INFO_DELIVER_CODE_MASK | INTR_INFO_VALID_MASK,
vcpu->arch.cr2);
return 1;
}

Using vcpu->arch.cr2 is suspicious as VMX doesn't update CR2 on VM
exits; isn't this going to change the CR2 visible in L2 guest after a
nested VM entry?

Btw. nested_vmx_check_exception() didn't support emulated exceptions at
all (it only passed through ones we got from hardware), or have I missed
something?

Thanks.