Re: [PATCH v6 11/13] KVM: s390: add functions to (un)register GISC with GISA

From: Michael Mueller
Date: Mon Jan 28 2019 - 12:16:04 EST



On 28.01.19 16:45, Pierre Morel wrote:
On 24/01/2019 13:59, Michael Mueller wrote:
Add the Interruption Alert Mask (IAM) to the architecture specific
kvm struct. This mask in the GISA is used to define for which ISC
a GIB alert will be issued.

The functions kvm_s390_gisc_register() and kvm_s390_gisc_unregister()
are used to (un)register a GISC (guest ISC) with a virtual machine and
its GISA.

Upon successful completion, kvm_s390_gisc_register() returns the
ISC to be used for GIB alert interruptions. A negative return code
indicates an error during registration.

Theses functions will be used by other adapter types like AP and PCI to
request pass-through interruption support.

Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
---
 arch/s390/include/asm/kvm_host.h | 13 +++++
 arch/s390/kvm/interrupt.c | 117 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 130 insertions(+)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 7077762ab460..2cfff617cb21 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -781,6 +781,9 @@ struct kvm_s390_gisa {
ÂÂÂÂÂÂÂÂÂÂÂÂÂ u8Â reserved03[11];
ÂÂÂÂÂÂÂÂÂÂÂÂÂ u32 airq_count;
ÂÂÂÂÂÂÂÂÂ } g1;
+ÂÂÂÂÂÂÂ struct {
+ÂÂÂÂÂÂÂÂÂÂÂ u64 word[4];
+ÂÂÂÂÂÂÂ } u64;
ÂÂÂÂÂ };
 };
@@ -813,8 +816,15 @@ struct kvm_s390_vsie {
ÂÂÂÂÂ struct page *pages[KVM_MAX_VCPUS];
 };
+struct kvm_s390_gisa_iam {
+ÂÂÂ u8 mask;
+ÂÂÂ spinlock_t ref_lock;
+ÂÂÂ u32 ref_count[MAX_ISC + 1];
+};
+
 struct kvm_s390_gisa_interrupt {
ÂÂÂÂÂ struct kvm_s390_gisa *origin;
+ÂÂÂ struct kvm_s390_gisa_iam alert;
 };
 struct kvm_arch{
@@ -885,6 +895,9 @@ void kvm_arch_crypto_set_masks(struct kvm *kvm, unsigned long *apm,
 extern int sie64a(struct kvm_s390_sie_block *, u64 *);
 extern char sie_exit;
+extern int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc);
+extern int kvm_s390_gisc_unregister(struct kvm *kvm, u32 gisc);
+
 static inline void kvm_arch_hardware_disable(void) {}
 static inline void kvm_arch_check_processor_compat(void *rtn) {}
 static inline void kvm_arch_sync_events(struct kvm *kvm) {}
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 5efcd9e2cf8f..6bc9dab6d352 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -222,6 +222,33 @@ static inline u8 int_word_to_isc(u32 int_word)
ÂÂ */
 #define IPM_BIT_OFFSET (offsetof(struct kvm_s390_gisa, ipm) * BITS_PER_BYTE)
+/**
+ * gisa_set_iam - change the GISA interruption alert mask
+ *
+ * @gisa: gisa to operate on
+ * @iam: new IAM value to use
+ *
+ * Change the IAM atomically with the next alert address and the IPM
+ * of the GISA if the GISA is not part of the GIB alert list. All three
+ * fields are located in the first long word of the GISA.
+ *
+ * Returns: 0 on success
+ *ÂÂÂÂÂÂÂÂÂ -EBUSY in case the gisa is part of the alert list
+ */
+static inline int gisa_set_iam(struct kvm_s390_gisa *gisa, u8 iam)
+{
+ÂÂÂ u64 word, _word;
+
+ÂÂÂ do {
+ÂÂÂÂÂÂÂ word = READ_ONCE(gisa->u64.word[0]);
+ÂÂÂÂÂÂÂ if ((u64)gisa != word >> 32)
+ÂÂÂÂÂÂÂÂÂÂÂ return -EBUSY;
+ÂÂÂÂÂÂÂ _word = (word & ~0xffUL) | iam;
+ÂÂÂ } while (cmpxchg(&gisa->u64.word[0], word, _word) != word);
+
+ÂÂÂ return 0;
+}
+
 static inline void gisa_set_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
 {
ÂÂÂÂÂ set_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
@@ -2911,6 +2938,8 @@ void kvm_s390_gisa_init(struct kvm *kvm)
ÂÂÂÂÂ if (!css_general_characteristics.aiv)
ÂÂÂÂÂÂÂÂÂ return;
ÂÂÂÂÂ gi->origin = &kvm->arch.sie_page2->gisa;
+ÂÂÂ gi->alert.mask = 0;
+ÂÂÂ spin_lock_init(&gi->alert.ref_lock);
ÂÂÂÂÂ kvm_s390_gisa_clear(kvm);
ÂÂÂÂÂ VM_EVENT(kvm, 3, "gisa 0x%pK initialized", gi->origin);
 }
@@ -2920,6 +2949,94 @@ void kvm_s390_gisa_destroy(struct kvm *kvm)
ÂÂÂÂÂ kvm->arch.gisa_int.origin = NULL;
 }
+/**
+ * kvm_s390_gisc_register - register a guest ISC
+ *
+ * @kvm:Â the kernel vm to work with
+ * @gisc: the guest interruption sub class to register
+ *
+ * The function extends the vm specific alert mask to use.
+ * The effectve IAM mask in the GISA is updated as well
+ * in case the GISA is not part of the GIB alert list.
+ * It will be updated latest when the IAM gets restored
+ * by gisa_get_ipm_or_restore_iam().
+ *
+ * Returns: the nonspecific ISC (NISC) the gib alert mechanism
+ *ÂÂÂÂÂÂÂÂÂ has registered with the channel subsystem.
+ *ÂÂÂÂÂÂÂÂÂ -ENODEV in case the vm uses no GISA
+ *ÂÂÂÂÂÂÂÂÂ -ERANGE in case the guest ISC is invalid
+ */
+int kvm_s390_gisc_register(struct kvm *kvm, u32 gisc)
+{
+ÂÂÂ struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
+ÂÂÂ u8 alert_mask;
+
+ÂÂÂ if (!gi->origin)
+ÂÂÂÂÂÂÂ return -ENODEV;
+ÂÂÂ if (gisc > MAX_ISC)
+ÂÂÂÂÂÂÂ return -ERANGE;
+
+ÂÂÂ spin_lock(&gi->alert.ref_lock);
+ÂÂÂ if (gi->alert.ref_count[gisc] == 0) {
+ÂÂÂÂÂÂÂ alert_mask = gi->alert.mask | 0x80 >> gisc;
+ÂÂÂÂÂÂÂ WRITE_ONCE(gi->alert.mask, alert_mask);

not sure WRITE_ONCE is useful.

I dropped that in both routines.




+ÂÂÂ }
+ÂÂÂ gi->alert.ref_count[gisc]++;
+ÂÂÂ if (gi->alert.ref_count[gisc] == 1)
+ÂÂÂÂÂÂÂ gisa_set_iam(gi->origin, alert_mask);

This will trigger a GAL interrupt on first AP interrupt in all cases.
However setting the iam here is simple and the price is not so high.
so... without the WRITE_ONCE in register and in unregister:



Acked-by: Pierre Morel<pmorel@xxxxxxxxxxxxx>

Pierre


Cheers,
Michael