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

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Message-ID: <f4c9634d-f442-447a-9eed-7d0f4e72c34f@redhat.com>
Date:   Thu, 23 Aug 2018 13:21:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Janosch Frank <frankja@...ux.ibm.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 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)

> 
>>
>> 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>

-- 

Thanks,

David / dhildenb