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

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Date:   Thu, 23 Aug 2018 13:33:50 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>,
        Pierre Morel <pmorel@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, cohuck@...hat.com,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        akrowiak@...ux.ibm.com, borntraeger@...ibm.com,
        schwidefsky@...ibm.com, heiko.carstens@...ibm.com
Subject: Re: [PATCH v3 3/3] KVM: s390: vsie: Make use of CRYCB FORMAT2 clear

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?

Code makes sense:
Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>

> 
>>
>>>
>>> When using FORMAT2 in the host we do not need to or with
>>> FORMAT1.
>>>
>>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>>> ---
>>>  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@...hat.com>
> 




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