On Fri, Jun 24, 2022 at 5:45 PM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
> ---
> 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;
This assignment should be above the comment, similar to vmx_vcpu_pi_load.
Uros.
> 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
>
