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KVM: s390: Remove one byte cmpxchg() usage

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Within sca_clear_ext_call() cmpxchg() is used to clear one or two bytes
(depending on sca format). The cmpxchg() calls are not supposed to fail; if
so that would be a bug. Given that cmpxchg() usage on one and two byte
areas generates very inefficient code, replace them with block concurrent
WRITE_ONCE() calls, and remove the WARN_ON().

Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Link: https://lore.kernel.org/r/20241126102515.3178914-3-hca@linux.ibm.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Heiko Carstens 2024-11-26 11:25:14 +01:00
parent 5618c53d96
commit 7061c63919
1 changed files with 2 additions and 11 deletions
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13
arch/s390/kvm/interrupt.c
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@ -118,8 +118,6 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id)
static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
{
int rc, expect;
if (!kvm_s390_use_sca_entries())
return;
kvm_s390_clear_cpuflags(vcpu, CPUSTAT_ECALL_PEND);
@ -128,23 +126,16 @@ static void sca_clear_ext_call(struct kvm_vcpu *vcpu)
struct esca_block *sca = vcpu->kvm->arch.sca;
union esca_sigp_ctrl *sigp_ctrl =
&(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
union esca_sigp_ctrl old;
old = READ_ONCE(*sigp_ctrl);
expect = old.value;
rc = cmpxchg(&sigp_ctrl->value, old.value, 0);
WRITE_ONCE(sigp_ctrl->value, 0);
} else {
struct bsca_block *sca = vcpu->kvm->arch.sca;
union bsca_sigp_ctrl *sigp_ctrl =
&(sca->cpu[vcpu->vcpu_id].sigp_ctrl);
union bsca_sigp_ctrl old;
old = READ_ONCE(*sigp_ctrl);
expect = old.value;
rc = cmpxchg(&sigp_ctrl->value, old.value, 0);
WRITE_ONCE(sigp_ctrl->value, 0);
}
read_unlock(&vcpu->kvm->arch.sca_lock);
WARN_ON(rc != expect); /* cannot clear? */
}
int psw_extint_disabled(struct kvm_vcpu *vcpu)