Re: [PATCH v5 11/15] KVM: s390: restore IAM in get_ipm() when IPM is clean

From: Michael Mueller
Date: Mon Jan 07 2019 - 13:17:26 EST

On 03.01.19 16:06, Pierre Morel wrote:
On 19/12/2018 20:17, Michael Mueller wrote:
The patch adds the parameter irq_flags and allows to
restore the Interruption Alert Mask (IAM) in the GISA
atomically while guaranteeing the IPM is clean.

The function returns the IPM of the GISA. If the returned
value is 0x00 and the IRQ_FLAG_IAM was set, the IAM has
been restored.

New irq flag:
ÂÂ IRQ_FLAG_IAM: When set, the IAM is restored if no ISC bit
ÂÂÂÂÂÂÂÂÂÂ is set in the IPM, i.e. no new airqs are
ÂÂÂÂÂÂÂ pending. The test and restore operations
ÂÂÂÂÂÂÂ are done atomically.

Signed-off-by: Michael Mueller <mimu@xxxxxxxxxxxxx>
 arch/s390/kvm/interrupt.c | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 1cc3ad2e6c7e..8307717e3caf 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -37,6 +37,7 @@
 #define IRQ_FLAG_LOCAL 0x8000 /* include local interruption pending mask */
 #define IRQ_FLAG_FLOATING 0x4000 /* include float interruption pending mask */
 #define IRQ_FLAG_GISA 0x2000 /* include GISA interruption pending mask */
+#define IRQ_FLAG_IAMÂÂÂÂÂ 0x0080 /* when set try to restore IAM */
@@ -253,9 +254,32 @@ static inline void set_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
ÂÂÂÂÂ set_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
-static inline u8 get_ipm(struct kvm_s390_gisa *gisa)
+static inline u8 get_ipm(struct kvm_s390_gisa *gisa, u16 irq_flags)
-ÂÂÂ return READ_ONCE(gisa->ipm);
+ÂÂÂ u64 word, _word;
+ÂÂÂ u8 ipm;
+ÂÂÂ if (!(irq_flags & IRQ_FLAG_IAM))
+ÂÂÂÂÂÂÂ return READ_ONCE(gisa->ipm);
+ÂÂÂ do {
+ÂÂÂÂÂÂÂ word = READ_ONCE(gisa->u64.word[0]);
+ÂÂÂÂÂÂÂ ipm = word >> 24;
+ÂÂÂÂÂÂÂ /* If the GISA is in the alert list, return the IPM. */
+ÂÂÂÂÂÂÂ if ((u64)gisa != word >> 32)
+ÂÂÂÂÂÂÂÂÂÂÂ return ipm;
+ÂÂÂÂÂÂÂ /* If the IPM is dirty, return the IPM. */
+ÂÂÂÂÂÂÂ if (ipm)
+ÂÂÂÂÂÂÂÂÂÂÂ return ipm;
+ÂÂÂÂÂÂÂÂ * Try to restore the IAM or loop, if the IPM is dirty
+ÂÂÂÂÂÂÂÂ * again or the GISA has been inserted into the alert list.
+ÂÂÂÂÂÂÂ _word = (word & ~0xffUL) |
+ÂÂÂÂÂÂÂÂÂÂÂ container_of(gisa, struct sie_page2, gisa)->kvm->arch.iam;
+ÂÂÂ } while (cmpxchg(&gisa->u64.word[0], word, _word) != _word);
+ÂÂÂ return 0;

Personal opinion, but this function do more than just getting the IPM, shouldn't it be reflected in the function name?

The main task of this function is to fetch the IPM. The additional
functionality is expressed in the flags.

A call like get_ipm_try_iam_restore(kvm, 0) would be more confusing.

 static inline void clear_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
@@ -277,7 +301,7 @@ static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu, u16 irq_flags)
ÂÂÂÂÂ if (irq_flags & IRQ_FLAG_FLOATING)
ÂÂÂÂÂÂÂÂÂ pending_irqs |= vcpu->kvm->arch.float_int.pending_irqs;
ÂÂÂÂÂ if (irq_flags & IRQ_FLAG_GISA)
-ÂÂÂÂÂÂÂ pending_irqs |= get_ipm(vcpu->kvm->arch.gisa) <<
+ÂÂÂÂÂÂÂ pending_irqs |= get_ipm(vcpu->kvm->arch.gisa, irq_flags) <<
ÂÂÂÂÂ return pending_irqs;
@@ -1574,7 +1598,7 @@ static int get_top_gisa_isc(struct kvm *kvm, u64 isc_mask, u32 schid)
ÂÂÂÂÂ if (!kvm->arch.gisa)
ÂÂÂÂÂÂÂÂÂ goto out;
-ÂÂÂ active_mask = (isc_mask & get_ipm(kvm->arch.gisa) << 24) << 32;
+ÂÂÂ active_mask = (isc_mask & get_ipm(kvm->arch.gisa, IRQ_FLAG_IAM) << 24) << 32;

why do we need to set the IAM here?

Yes, it should not be required, only when a vcpu goes into wait state.

ÂÂÂÂÂ while (active_mask) {
ÂÂÂÂÂÂÂÂÂ isc = __fls(active_mask) ^ (BITS_PER_LONG - 1);
ÂÂÂÂÂÂÂÂÂ if (tac_ipm_gisc(kvm->arch.gisa, isc))
@@ -2060,7 +2084,7 @@ static int get_all_floating_irqs(struct kvm *kvm, u8 __user *usrbuf, u64 len)
ÂÂÂÂÂ max_irqs = len / sizeof(struct kvm_s390_irq);
ÂÂÂÂÂ if (kvm->arch.gisa &&
-ÂÂÂÂÂÂÂ get_ipm(kvm->arch.gisa)) {
+ÂÂÂÂÂÂÂ get_ipm(kvm->arch.gisa, IRQ_FLAG_IAM)) {

and here?

Yes, it should not be required, only when a vcpu goes into wait state.

ÂÂÂÂÂÂÂÂÂ for (i = 0; i <= MAX_ISC; i++) {
ÂÂÂÂÂÂÂÂÂÂÂÂÂ if (n == max_irqs) {
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ /* signal userspace to try again */