linux-kernel - Re: [PATCH v3 04/10] KVM: arm64: vgic-its: Walk the LPI xarray in vgic_copy_lpi

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Date: Sun, 18 Feb 2024 10:28:19 +0000
From: Marc Zyngier <maz@...nel.org>
To: Zenghui Yu <yuzenghui@...wei.com>
Cc: Oliver Upton <oliver.upton@...ux.dev>,
	<kvmarm@...ts.linux.dev>,
	<kvm@...r.kernel.org>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose
	<suzuki.poulose@....com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 04/10] KVM: arm64: vgic-its: Walk the LPI xarray in vgic_copy_lpi_list()

On Sun, 18 Feb 2024 08:46:53 +0000,
Zenghui Yu <yuzenghui@...wei.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@...ux.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.

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.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.