>>> On 02.03.17 at 21:56, <julien.gr...@arm.com> wrote: > Ping? I'd like the question to be sorted out before Andre is sending a > new version. > > On 02/15/2017 09:25 PM, Stefano Stabellini wrote: >> On Wed, 15 Feb 2017, Julien Grall wrote: >>> Hi Stefano, >>> >>> On 14/02/17 21:00, Stefano Stabellini wrote: >>>> On Mon, 30 Jan 2017, Andre Przywara wrote: >>>>> +/* >>>>> + * Handle incoming LPIs, which are a bit special, because they are >>>>> potentially >>>>> + * numerous and also only get injected into guests. Treat them specially >>>>> here, >>>>> + * by just looking up their target vCPU and virtual LPI number and hand >>>>> it >>>>> + * over to the injection function. >>>>> + */ >>>>> +void do_LPI(unsigned int lpi) >>>>> +{ >>>>> + struct domain *d; >>>>> + union host_lpi *hlpip, hlpi; >>>>> + struct vcpu *vcpu; >>>>> + >>>>> + WRITE_SYSREG32(lpi, ICC_EOIR1_EL1); >>>>> + >>>>> + hlpip = gic_get_host_lpi(lpi); >>>>> + if ( !hlpip ) >>>>> + return; >>>>> + >>>>> + hlpi.data = read_u64_atomic(&hlpip->data); >>>>> + >>>>> + /* We may have mapped more host LPIs than the guest actually asked >>>>> for. */ >>>>> + if ( !hlpi.virt_lpi ) >>>>> + return; >>>>> + >>>>> + d = get_domain_by_id(hlpi.dom_id); >>>>> + if ( !d ) >>>>> + return; >>>>> + >>>>> + if ( hlpi.vcpu_id >= d->max_vcpus ) >>>>> + { >>>>> + put_domain(d); >>>>> + return; >>>>> + } >>>>> + >>>>> + vcpu = d->vcpu[hlpi.vcpu_id]; >>>>> + >>>>> + put_domain(d); >>>>> + >>>>> + vgic_vcpu_inject_irq(vcpu, hlpi.virt_lpi); >>>> >>>> put_domain should be here >>> >>> Why? I don't even understand why we would need to take a reference on the >>> domain for LPIs. Would not it be enough to use rcu_lock_domain_by_id here? >> >> I think that rcu_lock_domain_by_id would also work, but similarly we >> would need to call rcu_unlock here. >> >> To be honest, I don't know exactly in which cases get_domain should be >> used instead of rcu_lock_domain_by_id.
Aiui get_domain() is needed when you want to retain the reference across an operation that may involved blocking/scheduling. The RCU variant should be sufficient whenever you only need to make sure the domain won't go away for the duration of (a portion of) a function, since final domain destruction gets carried out from an RCU callback. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel