linux-kernel - Re: [PATCH v2 3/5] KVM: s390: vsie: Allow support for a host without AP

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Date:   Thu, 23 Aug 2018 08:52:57 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, cohuck@...hat.com,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        frankja@...ux.ibm.com, akrowiak@...ux.ibm.com,
        borntraeger@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH v2 3/5] KVM: s390: vsie: Allow support for a host without
 AP

On 22/08/2018 19:06, David Hildenbrand wrote:
> On 22.08.2018 18:51, Pierre Morel wrote:
>> Currently the CRYCB format used in the host for the
>> shadowed CRYCB is FORMAT2 while no check is done if
>> AP instructions are supported in the host.
>>
>> We better use the format the host calculated for the
>> guest 1 as the host already tested it against its
>> facility set.
>>
>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>> ---
>>   arch/s390/kvm/vsie.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
>> index 56a9d47..0b12916 100644
>> --- a/arch/s390/kvm/vsie.c
>> +++ b/arch/s390/kvm/vsie.c
>> @@ -154,6 +154,7 @@ static int shadow_crycb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>>   	const u32 crycb_addr = crycbd_o & 0x7ffffff8U;
>>   	unsigned long *b1, *b2;
>>   	u8 ecb3_flags;
>> +	unsigned long g1_fmt;
>>   
>>   	scb_s->crycbd = 0;
>>   	if (!(crycbd_o == CRYCB_FORMAT1))
>> @@ -180,8 +181,8 @@ 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;
>> +	g1_fmt = vcpu->arch.sie_block->crycbd & 0x03;
>> +	scb_s->crycbd = ((__u32)(__u64) &vsie_page->crycb) | g1_fmt;
>>   
>>   	/* xor both blocks in one run */
>>   	b1 = (unsigned long *) vsie_page->crycb.dea_wrapping_key_mask;
>>
> 
> This is wrong. I remember that with APXA, if FORMAT2 is available, we
> should always use FORMAT2. That's why we explicitly convert it here.
> 

You are right if FORMAT2 is available we should use FORMAT2
but the intention here is to use what KVM crypto init function did,
assuming it did the right thing.

Eventually we are running on a host without AP and we should use FORMAT1.

Isn't it correct?

Regards,
Pierre


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany