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Subject[PATCH] KVM: nVMX: clean up posted interrupt descriptor try_cmpxchg
Date
Rely on try_cmpxchg64 for re-reading the PID on failure, using READ_ONCE
only right before the first iteration.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/vmx/posted_intr.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c
index 73f60aa480fe..1b56c5e5c9fb 100644
--- a/arch/x86/kvm/vmx/posted_intr.c
+++ b/arch/x86/kvm/vmx/posted_intr.c
@@ -34,7 +34,7 @@ static inline struct pi_desc *vcpu_to_pi_desc(struct kvm_vcpu *vcpu)
return &(to_vmx(vcpu)->pi_desc);
}

-static int pi_try_set_control(struct pi_desc *pi_desc, u64 old, u64 new)
+static int pi_try_set_control(struct pi_desc *pi_desc, u64 *pold, u64 new)
{
/*
* PID.ON can be set at any time by a different vCPU or by hardware,
@@ -42,7 +42,7 @@ static int pi_try_set_control(struct pi_desc *pi_desc, u64 old, u64 new)
* update must be retried with a fresh snapshot an ON change causes
* the cmpxchg to fail.
*/
- if (!try_cmpxchg64(&pi_desc->control, &old, new))
+ if (!try_cmpxchg64(&pi_desc->control, pold, new))
return -EBUSY;

return 0;
@@ -96,8 +96,9 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
if (!x2apic_mode)
dest = (dest << 8) & 0xFF00;

+ old.control = READ_ONCE(pi_desc->control);
do {
- old.control = new.control = READ_ONCE(pi_desc->control);
+ new.control = old.control;

/*
* Clear SN (as above) and refresh the destination APIC ID to
@@ -111,7 +112,7 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
* descriptor was modified on "put" to use the wakeup vector.
*/
new.nv = POSTED_INTR_VECTOR;
- } while (pi_try_set_control(pi_desc, old.control, new.control));
+ } while (pi_try_set_control(pi_desc, &old.control, new.control));

local_irq_restore(flags);

@@ -156,12 +157,12 @@ static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu)

WARN(pi_desc->sn, "PI descriptor SN field set before blocking");

+ old.control = READ_ONCE(pi_desc->control);
do {
- old.control = new.control = READ_ONCE(pi_desc->control);
-
/* set 'NV' to 'wakeup vector' */
+ new.control = old.control;
new.nv = POSTED_INTR_WAKEUP_VECTOR;
- } while (pi_try_set_control(pi_desc, old.control, new.control));
+ } while (pi_try_set_control(pi_desc, &old.control, new.control));

/*
* Send a wakeup IPI to this CPU if an interrupt may have been posted
--
2.31.1
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