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

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Message-Id: <912d013c-c925-fb3e-ed1d-2d778a60c189@linux.ibm.com>
Date:   Thu, 23 Aug 2018 13:05:54 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Pierre Morel <pmorel@...ux.ibm.com>, david@...hat.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 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;

> 
> 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;
> 




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