Re: [PATCH v10 24/26] KVM: s390: device attrs to enable/disable AP interpretation

Tony Krowiak <akrowiak@xxxxxxxxxxxxx> · Mon, 24 Sep 2018 12:25:12 -0400

On 09/24/2018 07:23 AM, David Hildenbrand wrote:
On 22/09/2018 01:40, Tony Krowiak wrote:
On 09/17/2018 04:51 AM, David Hildenbrand wrote:
Am 12.09.18 um 21:43 schrieb Tony Krowiak:
From: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>

Introduces two new VM crypto device attributes (KVM_S390_VM_CRYPTO)
to enable or disable AP instruction interpretation from userspace
via the KVM_SET_DEVICE_ATTR ioctl:

* The KVM_S390_VM_CRYPTO_ENABLE_APIE attribute enables hardware
    interpretation of AP instructions executed on the guest.

* The KVM_S390_VM_CRYPTO_DISABLE_APIE attribute disables hardware
    interpretation of AP instructions executed on the guest. In this
    case the instructions will be intercepted and pass through to
    the guest.

Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
---
   arch/s390/include/asm/kvm_host.h |    1 +
   arch/s390/include/uapi/asm/kvm.h |    2 ++
   arch/s390/kvm/kvm-s390.c         |   27 +++++++++++++++++++++++----
   3 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index b32bd1b..36d3531 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -719,6 +719,7 @@ struct kvm_s390_crypto {
   	__u32 crycbd;
   	__u8 aes_kw;
   	__u8 dea_kw;
+	__u8 apie;
   };
   
   #define APCB0_MASK_SIZE 1
diff --git a/arch/s390/include/uapi/asm/kvm.h b/arch/s390/include/uapi/asm/kvm.h
index 8c23afc..a8dbd90 100644
--- a/arch/s390/include/uapi/asm/kvm.h
+++ b/arch/s390/include/uapi/asm/kvm.h
@@ -161,6 +161,8 @@ struct kvm_s390_vm_cpu_subfunc {
   #define KVM_S390_VM_CRYPTO_ENABLE_DEA_KW	1
   #define KVM_S390_VM_CRYPTO_DISABLE_AES_KW	2
   #define KVM_S390_VM_CRYPTO_DISABLE_DEA_KW	3
+#define KVM_S390_VM_CRYPTO_ENABLE_APIE		4
+#define KVM_S390_VM_CRYPTO_DISABLE_APIE		5
   
   /* kvm attributes for migration mode */
   #define KVM_S390_VM_MIGRATION_STOP	0
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 2cdd980..286c2e0 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -856,12 +856,11 @@ void kvm_s390_vcpu_crypto_reset_all(struct kvm *kvm)
   
   static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
   {
-	if (!test_kvm_facility(kvm, 76))
-		return -EINVAL;
-
   	mutex_lock(&kvm->lock);
   	switch (attr->attr) {
   	case KVM_S390_VM_CRYPTO_ENABLE_AES_KW:
+		if (!test_kvm_facility(kvm, 76))
+			return -EINVAL;
   		get_random_bytes(
   			kvm->arch.crypto.crycb->aes_wrapping_key_mask,
   			sizeof(kvm->arch.crypto.crycb->aes_wrapping_key_mask));
@@ -869,6 +868,8 @@ static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
   		VM_EVENT(kvm, 3, "%s", "ENABLE: AES keywrapping support");
   		break;
   	case KVM_S390_VM_CRYPTO_ENABLE_DEA_KW:
+		if (!test_kvm_facility(kvm, 76))
+			return -EINVAL;
   		get_random_bytes(
   			kvm->arch.crypto.crycb->dea_wrapping_key_mask,
   			sizeof(kvm->arch.crypto.crycb->dea_wrapping_key_mask));
@@ -876,17 +877,31 @@ static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
   		VM_EVENT(kvm, 3, "%s", "ENABLE: DEA keywrapping support");
   		break;
   	case KVM_S390_VM_CRYPTO_DISABLE_AES_KW:
+		if (!test_kvm_facility(kvm, 76))
+			return -EINVAL;
   		kvm->arch.crypto.aes_kw = 0;
   		memset(kvm->arch.crypto.crycb->aes_wrapping_key_mask, 0,
   			sizeof(kvm->arch.crypto.crycb->aes_wrapping_key_mask));
   		VM_EVENT(kvm, 3, "%s", "DISABLE: AES keywrapping support");
   		break;
   	case KVM_S390_VM_CRYPTO_DISABLE_DEA_KW:
+		if (!test_kvm_facility(kvm, 76))
+			return -EINVAL;
   		kvm->arch.crypto.dea_kw = 0;
   		memset(kvm->arch.crypto.crycb->dea_wrapping_key_mask, 0,
   			sizeof(kvm->arch.crypto.crycb->dea_wrapping_key_mask));
   		VM_EVENT(kvm, 3, "%s", "DISABLE: DEA keywrapping support");
   		break;
+	case KVM_S390_VM_CRYPTO_ENABLE_APIE:
+		if (!ap_instructions_available()) {
+			mutex_unlock(&kvm->lock);
+			return -EOPNOTSUPP;
+		}
+		kvm->arch.crypto.apie = 1;
+		break;
+	case KVM_S390_VM_CRYPTO_DISABLE_APIE:
+		kvm->arch.crypto.apie = 0;
+		break;
   	default:
   		mutex_unlock(&kvm->lock);
   		return -ENXIO;
@@ -1493,6 +1508,8 @@ static int kvm_s390_vm_has_attr(struct kvm *kvm, struct kvm_device_attr *attr)
   		case KVM_S390_VM_CRYPTO_ENABLE_DEA_KW:
   		case KVM_S390_VM_CRYPTO_DISABLE_AES_KW:
   		case KVM_S390_VM_CRYPTO_DISABLE_DEA_KW:
+		case KVM_S390_VM_CRYPTO_ENABLE_APIE:
+		case KVM_S390_VM_CRYPTO_DISABLE_APIE:

As also replied to the QEMU series, could we indicate
KVM_S390_VM_CRYPTO_ENABLE_APIE (and maybe
KVM_S390_VM_CRYPTO_DISABLE_APIE) only with ap_instructions_available(),
so we can avoid the additional KVM_S390_VM_CPU_FEAT_AP?

KVM_S390_VM_CPU_FEAT_AP is right now completely unused in KVM otherwise
(never checked, we only care about apie).

After much discussion with Halil and a few exchanges with you, we
decided to go ahead and accept your suggestion to get rid of
KVM_S390_VM_CPU_FEAT and keep the VM device attributes to enable/disable
apie.

To that end, I responded to patches 03/26, 11/26 and 25/26 with fixup!
patches that show the KVM/kernel changes that will be necessary to get
rid of KVM_S390_VM_CPU_FEAT and use apie to control ECA.28. I did that
to generate discussion in v10 rather than waiting until v11 for
comments. I make no guarantees that those fixup! patches will
successfully apply should you have a v10 branch generated from this
patch series you want to update.


Will you also fixup this patch to expose KVM_S390_VM_CRYPTO_ENABLE_APIE
only if supported by HW? (ap_instructions_available)

Given that this patch DOES expose KVM_S390_VM_CRYPTO_ENABLE_APIE only if 
supported by HW, I assume you are talking about
KVM_S390_VM_CRYPTO_DISABLE_APIE. I didn't check 
ap_instructions_available() for disabling APIE because I didn't
think it necessary given that ECA.28 will be set to 0 (intercept) by 
default, whether AP instructions are installed or not; so why not allow 
disabling apie. I suppose from the perspective of consistency, since the 
kvm_s390_vm_has_attr() function checks ap_instructions_available() for 
both attributes, then it probably makes sense to add that check to 
KVM_S390_VM_CRYPTO_DISABLE_APIE here. Then again, we could make a change 
in ap_instructions_available() to allow KVM_S390_VM_CRYPTO_DISABLE_APIE 
regardless of whether AP instructions are available. It boils down to 
whether APIE needs to be dynamically disabled at some point when it has 
been enabled. The only case I can think of where that may be necessary 
is if a guest is migrated to a system without AP instructions. I don't 
think that can happen and may even be protected against precisely 
because the VM attributes won't be available on the target system due to 
no AP instructions. What say you?









