[PATCH v2 3/9] KVM: s390: Fix get_all_floating_irqs()

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

When attempting to report all pending floating interrupt to userspace,
the GISA IPM bits are atomically tested and cleared, and the
corresponding interrupt description is written in the output buffer. If
the output buffer is too small, an error is returned to userspace, but
the GISA IPM bits are now lost.

Moreover, the contract of KVM_DEV_FLIC_GET_ALL_IRQS, which is the only
path to get_all_floating_irqs(), states that:

> All interrupts remain pending, i.e. are not deleted from the list of
> currently pending interrupts.

Fix by non-destructively testing for the GISA IPM bits.

Fixes: 24160af6cb28 ("KVM: s390: add GISA interrupts to FLIC ioctl interface")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/interrupt.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 6b3f97a7513b..61e75d10110e 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -273,6 +273,11 @@ static inline int gisa_tac_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
 	return test_and_clear_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *) gisa);
 }
 
+static inline int gisa_test_ipm_gisc(struct kvm_s390_gisa *gisa, u32 gisc)
+{
+	return test_bit_inv(IPM_BIT_OFFSET + gisc, (unsigned long *)gisa);
+}
+
 static inline unsigned long pending_irqs_no_gisa(struct kvm_vcpu *vcpu)
 {
 	unsigned long pending = vcpu->kvm->arch.float_int.pending_irqs |
@@ -2242,7 +2247,7 @@ static int get_all_floating_irqs(struct kvm *kvm, u8 __user *usrbuf, u64 len)
 				ret = -ENOMEM;
 				goto out_nolock;
 			}
-			if (gisa_tac_ipm_gisc(gi->origin, i)) {
+			if (gisa_test_ipm_gisc(gi->origin, i)) {
 				irq = (struct kvm_s390_irq *) &buf[n];
 				irq->type = KVM_S390_INT_IO(1, 0, 0, 0);
 				irq->u.io.io_int_word = isc_to_int_word(i);
-- 
2.55.0