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

[Vaibhav Jain <vaibhav@linux.ibm.com>]

"Aneesh Kumar K.V" <aneesh.kumar@kernel.org> writes:

> Vaibhav Jain <vaibhav@linux.ibm.com> writes:
>
>> Hi Aneesh,
>>
>> Thanks for looking into this patch. My responses inline below:
>>
>> "Aneesh Kumar K.V (IBM)" <aneesh.kumar@kernel.org> writes:
>>
>>> 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?
>>>
>> Thats right. However without this optimization the H_GUEST_DELETE hcall
>> in plpar_guest_delete() returns H_BUSY multiple times resulting in
>> multiple hcalls to the hypervisor until it finishes. Flushing the guest
>> translation cache upfront reduces the number of HCALLs L1 guests has to
>> make to delete a L2 guest via H_GUEST_DELETE.
>>
>
> can we add that as a comment above that kvmhv_flush_lpid()?
Sure, I will put up a comment with that detail in v2 of the patch
series.

>
> -aneesh

-- 
Cheers
~ Vaibhav