[PATCH v2] KVM: s390: Introduce storage key removal facility

Janosch Frank
2020-09-07T14:34:11Z

The storage key removal facility makes skey related instructions
result in special operation program exceptions. It is based on the
Keyless Subset Facility.

The usual suspects are iske, sske, rrbe and their respective
variants. lpsw(e), pfmf and tprot can also specify a key and essa with
an ORC of 4 will consult the change bit, hence they all result in
exceptions.

Unfortunately storage keys were so essential to the architecture, that
there is no facility bit that we could deactivate. That's why the
removal facility (bit 169) was introduced which makes it necessary,
that, if active, the skey related facilities 10, 14, 66, 145 and 149
are zero. Managing this requirement and migratability has to be done
in userspace, as KVM does not check the facilities it receives to be
able to easily implement userspace emulation.

Removing storage key support allows us to circumvent complicated
emulation code and makes huge page support tremendously easier.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---

v2:
* Removed the likely
* Updated and re-shuffeled the comments which had the wrong information

---
arch/s390/kvm/intercept.c | 40 ++++++++++++++++++++++++++++++++++++++-
arch/s390/kvm/kvm-s390.c | 5 +++++
arch/s390/kvm/priv.c | 26 ++++++++++++++++++++++---
3 files changed, 67 insertions(+), 4 deletions(-)

diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index e7a7c499a73f..983647ea2abe 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -33,6 +33,7 @@ u8 kvm_s390_get_ilen(struct kvm_vcpu *vcpu)
case ICPT_OPEREXC:
case ICPT_PARTEXEC:
case ICPT_IOINST:
+ case ICPT_KSS:
/* instruction only stored for these icptcodes */
ilen = insn_length(vcpu->arch.sie_block->ipa >> 8);
/* Use the length of the EXECUTE instruction if necessary */
@@ -565,7 +566,44 @@ int kvm_handle_sie_intercept(struct kvm_vcpu *vcpu)
rc = handle_partial_execution(vcpu);
break;
case ICPT_KSS:
- rc = kvm_s390_skey_check_enable(vcpu);
+ if (!test_kvm_facility(vcpu->kvm, 169)) {
+ rc = kvm_s390_skey_check_enable(vcpu);
+ } else {
+ /*
+ * Storage key removal facility emulation.
+ *
+ * KSS is the same priority as an instruction
+ * interception. Hence we need handling here
+ * and in the instruction emulation code.
+ *
+ * KSS is nullifying (no psw forward), SKRF
+ * issues suppressing SPECIAL OPS, so we need
+ * to forward by hand.
+ */
+ switch (vcpu->arch.sie_block->ipa) {
+ case 0xb2b2:
+ kvm_s390_forward_psw(vcpu, kvm_s390_get_ilen(vcpu));
+ rc = kvm_s390_handle_b2(vcpu);
+ break;
+ case 0x8200:
+ kvm_s390_forward_psw(vcpu, kvm_s390_get_ilen(vcpu));
+ rc = kvm_s390_handle_lpsw(vcpu);
+ break;
+ case 0:
+ /*
+ * Interception caused by a key in a
+ * exception new PSW mask. The guest
+ * PSW has already been updated to the
+ * non-valid PSW so we only need to
+ * inject a PGM.
+ */
+ rc = kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
+ break;
+ default:
+ kvm_s390_forward_psw(vcpu, kvm_s390_get_ilen(vcpu));
+ rc = kvm_s390_inject_program_int(vcpu, PGM_SPECIAL_OPERATION);
+ }
+ }
break;
case ICPT_MCHKREQ:
case ICPT_INT_ENABLE:
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 6b74b92c1a58..85647f19311d 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2692,6 +2692,11 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
/* we emulate STHYI in kvm */
set_kvm_facility(kvm->arch.model.fac_mask, 74);
set_kvm_facility(kvm->arch.model.fac_list, 74);
+ /* we emulate the storage key removal facility only with kss */
+ if (sclp.has_kss) {
+ set_kvm_facility(kvm->arch.model.fac_mask, 169);
+ set_kvm_facility(kvm->arch.model.fac_list, 169);
+ }
if (MACHINE_HAS_TLB_GUEST) {
set_kvm_facility(kvm->arch.model.fac_mask, 147);
set_kvm_facility(kvm->arch.model.fac_list, 147);
diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
index cd74989ce0b0..d1923fbec341 100644
--- a/arch/s390/kvm/priv.c
+++ b/arch/s390/kvm/priv.c
@@ -207,6 +207,13 @@ int kvm_s390_skey_check_enable(struct kvm_vcpu *vcpu)
int rc;

trace_kvm_s390_skey_related_inst(vcpu);
+
+ if (test_kvm_facility(vcpu->kvm, 169)) {
+ rc = kvm_s390_inject_program_int(vcpu, PGM_SPECIAL_OPERATION);
+ if (!rc)
+ return -EOPNOTSUPP;
+ }
+
/* Already enabled? */
if (vcpu->arch.skey_enabled)
return 0;
@@ -257,7 +264,7 @@ static int handle_iske(struct kvm_vcpu *vcpu)

rc = try_handle_skey(vcpu);
if (rc)
- return rc != -EAGAIN ? rc : 0;
+ return rc != (-EAGAIN || -EOPNOTSUPP) ? rc : 0;

kvm_s390_get_regs_rre(vcpu, &reg1, &reg2);

@@ -304,7 +311,7 @@ static int handle_rrbe(struct kvm_vcpu *vcpu)

rc = try_handle_skey(vcpu);
if (rc)
- return rc != -EAGAIN ? rc : 0;
+ return rc != (-EAGAIN || -EOPNOTSUPP) ? rc : 0;

kvm_s390_get_regs_rre(vcpu, &reg1, &reg2);

@@ -355,7 +362,7 @@ static int handle_sske(struct kvm_vcpu *vcpu)

rc = try_handle_skey(vcpu);
if (rc)
- return rc != -EAGAIN ? rc : 0;
+ return rc != (-EAGAIN || -EOPNOTSUPP) ? rc : 0;

if (!test_kvm_facility(vcpu->kvm, 8))
m3 &= ~SSKE_MB;
@@ -745,6 +752,8 @@ int kvm_s390_handle_lpsw(struct kvm_vcpu *vcpu)
return kvm_s390_inject_prog_cond(vcpu, rc);
if (!(new_psw.mask & PSW32_MASK_BASE))
return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
+ if (new_psw.mask & PSW32_MASK_KEY && test_kvm_facility(vcpu->kvm, 169))
+ return kvm_s390_inject_program_int(vcpu, PGM_SPECIAL_OPERATION);
gpsw->mask = (new_psw.mask & ~PSW32_MASK_BASE) << 32;
gpsw->mask |= new_psw.addr & PSW32_ADDR_AMODE;
gpsw->addr = new_psw.addr & ~PSW32_ADDR_AMODE;
@@ -771,6 +780,8 @@ static int handle_lpswe(struct kvm_vcpu *vcpu)
rc = read_guest(vcpu, addr, ar, &new_psw, sizeof(new_psw));
if (rc)
return kvm_s390_inject_prog_cond(vcpu, rc);
+ if ((new_psw.mask & PSW_MASK_KEY) && test_kvm_facility(vcpu->kvm, 169))
+ return kvm_s390_inject_program_int(vcpu, PGM_SPECIAL_OPERATION);
vcpu->arch.sie_block->gpsw = new_psw;
if (!is_valid_psw(&vcpu->arch.sie_block->gpsw))
return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
@@ -1025,6 +1036,10 @@ static int handle_pfmf(struct kvm_vcpu *vcpu)
if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);

+ if (vcpu->run->s.regs.gprs[reg1] & PFMF_SK &&
+ test_kvm_facility(vcpu->kvm, 169))
+ return kvm_s390_inject_program_int(vcpu, PGM_SPECIAL_OPERATION);
+
if (vcpu->run->s.regs.gprs[reg1] & PFMF_RESERVED)
return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);

@@ -1203,6 +1218,8 @@ static int handle_essa(struct kvm_vcpu *vcpu)
return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
/* Check for invalid operation request code */
orc = (vcpu->arch.sie_block->ipb & 0xf0000000) >> 28;
+ if (orc == ESSA_SET_POT_VOLATILE && test_kvm_facility(vcpu->kvm, 169))
+ return kvm_s390_inject_program_int(vcpu, PGM_SPECIAL_OPERATION);
/* ORCs 0-6 are always valid */
if (orc > (test_kvm_facility(vcpu->kvm, 147) ? ESSA_SET_STABLE_NODAT
: ESSA_SET_STABLE_IF_RESIDENT))
@@ -1451,6 +1468,9 @@ static int handle_tprot(struct kvm_vcpu *vcpu)

kvm_s390_get_base_disp_sse(vcpu, &address1, &address2, &ar, NULL);

+ if ((address2 & 0xf0) && test_kvm_facility(vcpu->kvm, 169))
+ return kvm_s390_inject_program_int(vcpu, PGM_SPECIAL_OPERATION);
+
/* we only handle the Linux memory detection case:
* access key == 0
* everything else goes to userspace. */
--
2.25.1