Re: [PATCH v5 16/23] irqchip/gic-v4.1: Eagerly vmap vPEs

[Zenghui Yu]

Hi Marc,

On 2020/3/19 18:55, Marc Zyngier wrote:
> On 2020-03-17 02:49, Zenghui Yu wrote:
> > Hi Marc,
> >
> > On 2020/3/5 4:33, Marc Zyngier wrote:
> > > Now that we have HW-accelerated SGIs being delivered to VPEs, it
> > > becomes required to map the VPEs on all ITSs instead of relying
> > > on the lazy approach that we would use when using the ITS-list
> > > mechanism.
> > >
> > > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> >
> > Before GICv4.1, we use vlpi_count to evaluate whether the vPE has been
> > mapped on the specified ITS, and use this refcount to only issue VMOVP
> > to those involved ITSes. It's broken after this patch.
> >
> > We may need to re-evaluate "whether the vPE is mapped" now that we're at
> > GICv4.1, otherwise *no* VMOVP will be issued on the v4.1 capable machine
> > (I mean those without single VMOVP support).
> >
> > What I'm saying is something like below (only an idea, it even can't
> > compile), any thoughts?
> >
> >
> > diff --git a/drivers/irqchip/irq-gic-v3-its.c 
> > b/drivers/irqchip/irq-gic-v3-its.c
> > index 2e12bc52e3a2..3450b5e847ca 100644
> > --- a/drivers/irqchip/irq-gic-v3-its.c
> > +++ b/drivers/irqchip/irq-gic-v3-its.c
> > @@ -198,7 +198,8 @@ static u16 get_its_list(struct its_vm *vm)
> > ÂÂÂÂÂÂÂÂ if (!is_v4(its))
> > ÂÂÂÂÂÂÂÂÂÂÂÂ continue;
> >
> > -ÂÂÂÂÂÂÂ if (vm->vlpi_count[its->list_nr])
> > +ÂÂÂÂÂÂÂ if (vm->vlpi_count[its->list_nr] ||
> > +ÂÂÂÂÂÂÂÂÂÂÂ gic_requires_eager_mapping())
> > ÂÂÂÂÂÂÂÂÂÂÂÂ __set_bit(its->list_nr, &its_list);
> > ÂÂÂÂ }
> >
> > @@ -1295,7 +1296,8 @@ static void its_send_vmovp(struct its_vpe *vpe)
> > ÂÂÂÂÂÂÂÂ if (!is_v4(its))
> > ÂÂÂÂÂÂÂÂÂÂÂÂ continue;
> >
> > -ÂÂÂÂÂÂÂ if (!vpe->its_vm->vlpi_count[its->list_nr])
> > +ÂÂÂÂÂÂÂ if (!vpe->its_vm->vlpi_count[its->list_nr] &&
> > +ÂÂÂÂÂÂÂÂÂÂÂ !gic_requires_eager_mapping())
> > ÂÂÂÂÂÂÂÂÂÂÂÂ continue;
> >
> > ÂÂÂÂÂÂÂÂ desc.its_vmovp_cmd.col = &its->collections[col_id];
>
> It took me a while to wrap my head around that one, but you're as usual 
> spot on.
>
> The use of gic_requires_eager_mapping() is a bit confusing here, as it 
> isn't
> so much that the VPE is eagerly mapped, but the predicate on which we 
> evaluate
> the need for a VMOVP. How about this:
>
> diff --git a/drivers/irqchip/irq-gic-v3-its.c 
> b/drivers/irqchip/irq-gic-v3-its.c
> index cd6451e190c9..348f7a909a69 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -189,6 +189,15 @@ static DEFINE_IDA(its_vpeid_ida);
>  Â#define gic_data_rdist_rd_base()ÂÂÂ (gic_data_rdist()->rd_base)
>  Â#define gic_data_rdist_vlpi_base()ÂÂÂ (gic_data_rdist_rd_base() + 
> SZ_128K)
>
> +/*
> + * Skip ITSs that have no vLPIs mapped, unless we're on GICv4.1, as we
> + * always have vSGIs mapped.
> + */
> +static bool require_its_list_vmovp(struct its_vm *vm, struct its_node 
> *its)
> +{
> +ÂÂÂ return (gic_rdists->has_rvpeid || vm->vlpi_count[its->list_nr]);
> +}
> +
>  Âstatic u16 get_its_list(struct its_vm *vm)
>  Â{
>  ÂÂÂÂ struct its_node *its;
> @@ -198,7 +207,7 @@ static u16 get_its_list(struct its_vm *vm)
>  ÂÂÂÂÂÂÂÂ if (!is_v4(its))
>  ÂÂÂÂÂÂÂÂÂÂÂÂ continue;
>
> -ÂÂÂÂÂÂÂ if (vm->vlpi_count[its->list_nr])
> +ÂÂÂÂÂÂÂ if (require_its_list_vmovp(vm, its))
>  ÂÂÂÂÂÂÂÂÂÂÂÂ __set_bit(its->list_nr, &its_list);
>  ÂÂÂÂ }
>
> @@ -1295,7 +1304,7 @@ static void its_send_vmovp(struct its_vpe *vpe)
>  ÂÂÂÂÂÂÂÂ if (!is_v4(its))
>  ÂÂÂÂÂÂÂÂÂÂÂÂ continue;
>
> -ÂÂÂÂÂÂÂ if (!vpe->its_vm->vlpi_count[its->list_nr])
> +ÂÂÂÂÂÂÂ if (!require_its_list_vmovp(vpe->its_vm, its))
>  ÂÂÂÂÂÂÂÂÂÂÂÂ continue;
>
>  ÂÂÂÂÂÂÂÂ desc.its_vmovp_cmd.col = &its->collections[col_id];

Indeed this looks much clearer. We're actually evaluating the need
for issuing VMOVP to a specified ITS, on system using its_list_map
feature (though we evaluate it by checking whether the vPE is mapped
on this ITS).


Thanks,
Zenghui