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

From: Pierre Morel
Date: Thu Aug 23 2018 - 07:47:32 EST

On 23/08/2018 13:33, Janosch Frank wrote:
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

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?

yes, done, I modified the comment in front of the function.

Code makes sense:
Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>



When using FORMAT2 in the host we do not need to or with

Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
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 |
+ 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@xxxxxxxxxx>

Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany