Re: [PATCH 19/32] KVM: s390: mechanism to enable guest zPCI Interpretation

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On 12/10/21 8:27 AM, Christian Borntraeger wrote:


Am 07.12.21 um 21:57 schrieb Matthew Rosato:
The guest must have access to certain facilities in order to allow
interpretive execution of zPCI instructions and adapter event
notifications.  However, there are some cases where a guest might
disable interpretation -- provide a mechanism via which we can defer
enabling the associated zPCI interpretation facilities until the guest
indicates it wishes to use them.

Signed-off-by: Matthew Rosato <mjrosato@xxxxxxxxxxxxx>
---
  arch/s390/include/asm/kvm_host.h |  4 +++
  arch/s390/kvm/kvm-s390.c         | 43 ++++++++++++++++++++++++++++++++
  arch/s390/kvm/kvm-s390.h         | 10 ++++++++
  3 files changed, 57 insertions(+)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 3f147b8d050b..38982c1de413 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -252,7 +252,10 @@ struct kvm_s390_sie_block {
  #define ECB2_IEP    0x20
  #define ECB2_PFMFI    0x08
  #define ECB2_ESCA    0x04
+#define ECB2_ZPCI_LSI    0x02
      __u8    ecb2;                   /* 0x0062 */
+#define ECB3_AISI    0x20
+#define ECB3_AISII    0x10
  #define ECB3_DEA 0x08
  #define ECB3_AES 0x04
  #define ECB3_RI  0x01
@@ -938,6 +941,7 @@ struct kvm_arch{
      int use_cmma;
      int use_pfmfi;
      int use_skf;
+    int use_zpci_interp;
      int user_cpu_state_ctrl;
      int user_sigp;
      int user_stsi;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index a680f2a02b67..361d742cdf0d 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1023,6 +1023,47 @@ static int kvm_s390_vm_set_crypto(struct kvm *kvm, struct kvm_device_attr *attr)
      return 0;
  }
+static void kvm_s390_vcpu_pci_setup(struct kvm_vcpu *vcpu)
+{
+    /*
+     * If the facilities aren't available for PCI interpretation and
+     * interrupt forwarding, we shouldn't be here.
+     */

This reads like we want a WARN_ON or BUG_ON, but as we call this uncoditionally this is actually a valid check. So instead of "shouldn't be here" say something like "bail out
if interpretion is not active".  ?

Right, this comment block is plain wrong. We expect to get here under multiple circumstances and its OK for this bit to be off:
- initial vcpu setup (use_zpci_interp is off)
- Right after we set use_zpci_interp=1 (turn on ECB for all vcpu)
- hotplug vcpu setup (use_zpci_interp might be on or off)

Will re-word.


+    if (!vcpu->kvm->arch.use_zpci_interp)
+        return;
+
+    vcpu->arch.sie_block->ecb2 |= ECB2_ZPCI_LSI;
+    vcpu->arch.sie_block->ecb3 |= ECB3_AISII + ECB3_AISI;
+}
+
+void kvm_s390_vcpu_pci_enable_interp(struct kvm *kvm)
+{
+    struct kvm_vcpu *vcpu;
+    int i;
+
+    /*
+     * If host facilities are available, turn on interpretation for the
+     * life of this guest
+     */
+    if (!test_facility(69) || !test_facility(70) || !test_facility(71) ||
+        !test_facility(72))
+        return;

Wouldnt that also enable interpretion for VSIE? I guess we should check for the
sclp facilities from patches 1,2,3, and 4 instead.


Good point -- will change.





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