Re: [PATCH v3 3/3] KVM: s390: vsie: Make use of CRYCB FORMAT2 clear

[Janosch Frank]

On 8/23/18 1:47 PM, Pierre Morel wrote:
> On 23/08/2018 13:33, Janosch Frank wrote:
>> On 8/23/18 1:21 PM, David Hildenbrand wrote:
>>> On 23.08.2018 13:05, Janosch Frank wrote:
>>>> On 8/23/18 12:25 PM, Pierre Morel wrote:
>>>>> The comment preceding the shadow_crycb function is
>>>>> misleading, we effectively accept FORMAT2 CRYCB in the
>>>>> guest.
>>>>
>>>> I beg to differ:
>>>>
>>>> if (!(crycbd_o & vcpu->arch.sie_block->crycbd & CRYCB_FORMAT1))
>>>> 		return 0;
>>>
>>> FORMAT2 includes bit FORMAT1 (backwards compatible)
>>
>> Right, this check is very misleading because of the constant, we
>> effectively test against Format 0 and Format 2.
>>
>> Can we make this clearer by explicitly ANDing 0x01 or adding a comment?
> 
> yes, done, I modified the comment in front of the function.

Which is not what I want, what I want is:

/* CRYCB_FORMAT2 includes the bit for CRYCB_FORMAT1, so we allow both
formats here */
if (!(crycbd_o & vcpu->arch.sie_block->crycbd & CRYCB_FORMAT1))
	return 0;

> 
>>
>> Code makes sense:
>> Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
> 
> Thanks,
> 
> regards,
> Pierre
> 
>>
>>>
>>>>
>>>>>
>>>>> When using FORMAT2 in the host we do not need to or with
>>>>> FORMAT1.
>>>>>
>>>>> Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
>>>>> ---
>>>>>   arch/s390/kvm/vsie.c | 6 +++---
>>>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
>>>>> index 38ea5da..e0e6fbf 100644
>>>>> --- a/arch/s390/kvm/vsie.c
>>>>> +++ b/arch/s390/kvm/vsie.c
>>>>> @@ -140,7 +140,8 @@ static int prepare_cpuflags(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>>>>>    * Create a shadow copy of the crycb block and setup key wrapping, if
>>>>>    * requested for guest 3 and enabled for guest 2.
>>>>>    *
>>>>> - * We only accept format-1 (no AP in g2), but convert it into format-2
>>>>> + * We accept format-1 or format-2, but we treat it as a format-1 (no AP in g2),
>>>>> + * and we convert it into format-2 in the shadow CRYCB.
>>>>>    * There is nothing to do for format-0.
>>>>>    *
>>>>>    * Returns: - 0 if shadowed or nothing to do
>>>>> @@ -179,8 +180,7 @@ static int shadow_crycb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>>>>>   		return set_validity_icpt(scb_s, 0x0035U);
>>>>>   
>>>>>   	scb_s->ecb3 |= ecb3_flags;
>>>>> -	scb_s->crycbd = ((__u32)(__u64) &vsie_page->crycb) | CRYCB_FORMAT1 |
>>>>> -			CRYCB_FORMAT2;
>>>>> +	scb_s->crycbd = ((__u32)(__u64) &vsie_page->crycb) | CRYCB_FORMAT2;
>>>>
>>>> That's purely cosmetic but valid.
>>>>
>>>>>   
>>>>>   	/* xor both blocks in one run */
>>>>>   	b1 = (unsigned long *) vsie_page->crycb.dea_wrapping_key_mask;
>>>
>>> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
>>>
>>
>>
> 
>

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