Re: [PATCH V2 1/2] KVM/VMX: Check ept_pointer before flushing ept tlb

[Paolo Bonzini <pbonzini@redhat.com>]

On 06/12/18 08:34, lantianyu1986@gmail.com wrote:
> From: Lan Tianyu <Tianyu.Lan@microsoft.com>
> 
> This patch is to initialize ept_pointer to INVALID_PAGE and check it
> before flushing ept tlb. If ept_pointer is invalid, bypass the flush
> request.
> 
> Signed-off-by: Lan Tianyu <Tianyu.Lan@microsoft.com>

Can you explain better *why* this patch is needed?  Also, should
vmx->ept_pointer be cleared at reset time, rather than vCPU creation?

Thanks,

Paolo

> ---
>  arch/x86/kvm/vmx.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index c379d0bfdcba..6577ec8cbb0f 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -1582,11 +1582,18 @@ static int vmx_hv_remote_flush_tlb(struct kvm *kvm)
>  	/*
>  	 * FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE hypercall needs the address of the
>  	 * base of EPT PML4 table, strip off EPT configuration information.
> +	 * If ept_pointer is invalid pointer, bypass the flush request.
>  	 */
>  	if (to_kvm_vmx(kvm)->ept_pointers_match != EPT_POINTERS_MATCH) {
> -		kvm_for_each_vcpu(i, vcpu, kvm)
> +		kvm_for_each_vcpu(i, vcpu, kvm) {
> +			u64 ept_pointer = to_vmx(vcpu)->ept_pointer;
> +
> +			if (!VALID_PAGE(ept_pointer))
> +				continue;
> +
>  			ret |= hyperv_flush_guest_mapping(
> -				to_vmx(kvm_get_vcpu(kvm, i))->ept_pointer & PAGE_MASK);
> +				ept_pointer & PAGE_MASK);
> +		}
>  	} else {
>  		ret = hyperv_flush_guest_mapping(
>  				to_vmx(kvm_get_vcpu(kvm, 0))->ept_pointer & PAGE_MASK);
> @@ -11614,6 +11621,8 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>  	vmx->pi_desc.nv = POSTED_INTR_VECTOR;
>  	vmx->pi_desc.sn = 1;
>  
> +	vmx->ept_pointer = INVALID_PAGE;
> +
>  	return &vmx->vcpu;
>  
>  free_vmcs:
>