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Re: [Xen-devel] [PATCH 11/28] ARM: GICv3: forward pending LPIs to guests
Hi Jan,
On 03/03/17 07:58, Jan Beulich wrote:
On 02.03.17 at 21:56, <julien.grall@xxxxxxx> 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.
Thank you for explanation. I think it makes sense. There will be no
scheduling or softirq_pending involves in do_LPI so using
rcu_lock_domain_by_id seems more suitable here.
Cheers,
--
Julien Grall
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