Re: [PATCH 01/12] KVM: PPC: Book3S HV nestedv2: Invalidate RPT before deleting a guest

[Aneesh Kumar K.V (IBM) <aneesh.kumar@kernel.org>]

Vaibhav Jain <vaibhav@linux.ibm.com> writes:

> From: Jordan Niethe <jniethe5@gmail.com>
>
> An L0 must invalidate the L2's RPT during H_GUEST_DELETE if this has not
> already been done. This is a slow operation that means H_GUEST_DELETE
> must return H_BUSY multiple times before completing. Invalidating the
> tables before deleting the guest so there is less work for the L0 to do.
>
> Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> ---
>  arch/powerpc/include/asm/kvm_book3s.h | 1 +
>  arch/powerpc/kvm/book3s_hv.c          | 6 ++++--
>  arch/powerpc/kvm/book3s_hv_nested.c   | 2 +-
>  3 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
> index 4f527d09c92b..a37736ed3728 100644
> --- a/arch/powerpc/include/asm/kvm_book3s.h
> +++ b/arch/powerpc/include/asm/kvm_book3s.h
> @@ -302,6 +302,7 @@ void kvmhv_nested_exit(void);
>  void kvmhv_vm_nested_init(struct kvm *kvm);
>  long kvmhv_set_partition_table(struct kvm_vcpu *vcpu);
>  long kvmhv_copy_tofrom_guest_nested(struct kvm_vcpu *vcpu);
> +void kvmhv_flush_lpid(u64 lpid);
>  void kvmhv_set_ptbl_entry(u64 lpid, u64 dw0, u64 dw1);
>  void kvmhv_release_all_nested(struct kvm *kvm);
>  long kvmhv_enter_nested_guest(struct kvm_vcpu *vcpu);
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 1ed6ec140701..5543e8490cd9 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -5691,10 +5691,12 @@ static void kvmppc_core_destroy_vm_hv(struct kvm *kvm)
>  			kvmhv_set_ptbl_entry(kvm->arch.lpid, 0, 0);
>  	}
>  
> -	if (kvmhv_is_nestedv2())
> +	if (kvmhv_is_nestedv2()) {
> +		kvmhv_flush_lpid(kvm->arch.lpid);
>  		plpar_guest_delete(0, kvm->arch.lpid);
>

I am not sure I follow the optimization here. I would expect the
hypervisor to kill all the translation caches as part of guest_delete.
What is the benefit of doing a lpid flush outside the guest delete?

> -	else
> +	} else {
>  		kvmppc_free_lpid(kvm->arch.lpid);
> +	}
>  
>  	kvmppc_free_pimap(kvm);
>  }
> diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
> index 3b658b8696bc..5c375ec1a3c6 100644
> --- a/arch/powerpc/kvm/book3s_hv_nested.c
> +++ b/arch/powerpc/kvm/book3s_hv_nested.c
> @@ -503,7 +503,7 @@ void kvmhv_nested_exit(void)
>  	}
>  }
>  
> -static void kvmhv_flush_lpid(u64 lpid)
> +void kvmhv_flush_lpid(u64 lpid)
>  {
>  	long rc;
>  
> -- 
> 2.42.0