linux-kernel - Re: [PATCH v2 2/5] KVM: s390: vsie: Only accept FORMAT1 CRYCB for guest2

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Date:   Wed, 22 Aug 2018 18:55:46 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Pierre Morel <pmorel@...ux.ibm.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 2/5] KVM: s390: vsie: Only accept FORMAT1 CRYCB for
 guest2

On 22.08.2018 18:51, Pierre Morel wrote:
> As the comment above the function suggested the shadowing
> of the guest2 CRYCB can only accept a format 1 since
> AP instructions are not supported in the guest.
> 
> Let's modify the check which allowed to accept a format 2 too.

As the bit is ignored without AP/APXA, it is perfectly valid to accept a
format 2, we just have to interpret it as format 1 (which is what we do)

What am I missing?

> 
> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
> ---
>  arch/s390/kvm/vsie.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 12b9707..56a9d47 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -156,7 +156,9 @@ static int shadow_crycb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  	u8 ecb3_flags;
>  
>  	scb_s->crycbd = 0;
> -	if (!(crycbd_o & vcpu->arch.sie_block->crycbd & CRYCB_FORMAT1))
> +	if (!(crycbd_o == CRYCB_FORMAT1))
> +		return 0;

huh, this looks very broken. The address is still in there.

> +	if (!(vcpu->arch.sie_block->crycbd & CRYCB_FORMAT1))
>  		return 0;
>  	/* format-1 is supported with message-security-assist extension 3 */
>  	if (!test_kvm_facility(vcpu->kvm, 76))
> 


-- 

Thanks,

David / dhildenb