Re: [PATCH v3 04/10] KVM: arm64: vgic-its: Walk the LPI xarray in vgic_copy_lpi_list()

Oliver Upton
2024-02-18T18:05:44Z

On Sun, Feb 18, 2024 at 10:28:19AM +0000, Marc Zyngier wrote:
> On Sun, 18 Feb 2024 08:46:53 +0000,
> Zenghui Yu <yuzenghui@huawei.com> wrote:
> >
> > On 2024/2/17 2:41, Oliver Upton wrote:
> > > Start iterating the LPI xarray in anticipation of removing the LPI
> > > linked-list.
> > >
> > > Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
> > > ---
> > > arch/arm64/kvm/vgic/vgic-its.c | 7 ++++++-
> > > 1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
> > > index fb2d3c356984..9ce2edfadd11 100644
> > > --- a/arch/arm64/kvm/vgic/vgic-its.c
> > > +++ b/arch/arm64/kvm/vgic/vgic-its.c
> > > @@ -335,6 +335,7 @@ static int update_lpi_config(struct kvm *kvm, struct vgic_irq *irq,
> > > int vgic_copy_lpi_list(struct kvm *kvm, struct kvm_vcpu *vcpu, u32 **intid_ptr)
> > > {
> > > struct vgic_dist *dist = &kvm->arch.vgic;
> > > + XA_STATE(xas, &dist->lpi_xa, GIC_LPI_OFFSET);
> > > struct vgic_irq *irq;
> > > unsigned long flags;
> > > u32 *intids;
> > > @@ -353,7 +354,9 @@ int vgic_copy_lpi_list(struct kvm *kvm, struct kvm_vcpu *vcpu, u32 **intid_ptr)
> > > return -ENOMEM;
> > > raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
> > > - list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) {
> > > + rcu_read_lock();
> > > +
> > > + xas_for_each(&xas, irq, INTERRUPT_ID_BITS_ITS) {
> >
> > We should use '1 << INTERRUPT_ID_BITS_ITS - 1' to represent the maximum
> > LPI interrupt ID.

/facepalm

Thanks Zenghui!

> Huh, well caught! I'm not even sure how it works, as that's way
> smaller than the start of the walk (8192). Probably doesn't.
>
> An alternative would be to use max_lpis_propbaser(), but I'm not sure
> we always have a valid PROPBASER value set when we start using this
> function. Worth investigating though.

Given the plans to eventually replace this with xarray marks, I'd vote
for doing the lazy thing and deciding this at compile time.

I can squash this in when I apply the series if the rest of it isn't
offensive, otherwise respin with the change.

--
Thanks,
Oliver

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index d84cb7618c59..f6025886071c 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -316,6 +316,8 @@ static int update_lpi_config(struct kvm *kvm, struct vgic_irq *irq,
return 0;
}

+#define GIC_LPI_MAX_INTID ((1 << INTERRUPT_ID_BITS_ITS) - 1)
+
/*
* Create a snapshot of the current LPIs targeting @vcpu, so that we can
* enumerate those LPIs without holding any lock.
@@ -345,7 +347,7 @@ int vgic_copy_lpi_list(struct kvm *kvm, struct kvm_vcpu *vcpu, u32 **intid_ptr)
raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
rcu_read_lock();

- xas_for_each(&xas, irq, INTERRUPT_ID_BITS_ITS) {
+ xas_for_each(&xas, irq, GIC_LPI_MAX_INTID) {
if (i == irq_count)
break;
/* We don't need to "get" the IRQ, as we hold the list lock. */