Re: [PATCH v12 1/7] irqchip/gic-v3: Enable support for SGIs to act as NMIs

[Doug Anderson]

Hi,

On Thu, Aug 31, 2023 at 1:53 AM Mark Rutland <mark.rutland@xxxxxxx> wrote:
>
> On Wed, Aug 30, 2023 at 12:11:22PM -0700, Douglas Anderson wrote:
> > As of commit 6abbd6988971 ("irqchip/gic, gic-v3: Make SGIs use
> > handle_percpu_devid_irq()") SGIs are treated the same as PPIs/EPPIs
> > and use handle_percpu_devid_irq() by default. Unfortunately,
> > handle_percpu_devid_irq() isn't NMI safe, and so to run in an NMI
> > context those should use handle_percpu_devid_fasteoi_nmi().
> >
> > In order to accomplish this, we just have to make room for SGIs in the
> > array of refcounts that keeps track of which interrupts are set as
> > NMI. We also rename the array and create a new indexing scheme that
> > accounts for SGIs.
> >
> > Also, enable NMI support prior to gic_smp_init() as allocation of SGIs
> > as IRQs/NMIs happen as part of this routine.
> >
> > Co-developed-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> > Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> > ---
> > I'll note that this change is a little more black magic to me than
> > others in this series. I don't have a massive amounts of familiarity
> > with all the moving parts of gic-v3, so I mostly just followed Mark
> > Rutland's advice [1]. Please pay extra attention to make sure I didn't
> > do anything too terrible.
> >
> > Mark's advice wasn't a full patch and I ended up doing a bit of work
> > to translate it to reality, so I did not add him as "Co-developed-by"
> > here. Mark: if you would like this tag then please provide it and your
> > Signed-off-by. I certainly won't object.
>
> That's all reasonable, and I'm perfectly happy without a tag.
>
> I have one trivial nit below, but with or without that fixed up:
>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
>
> >
> > [1] https://lore.kernel.org/r/ZNC-YRQopO0PaIIo@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > Changes in v12:
> > - Added a comment about why we account for 16 SGIs when Linux uses 8.
> >
> > Changes in v10:
> > - Rewrite as needed for 5.11+ as per Mark Rutland and Sumit.
> >
> >  drivers/irqchip/irq-gic-v3.c | 59 +++++++++++++++++++++++++-----------
> >  1 file changed, 41 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> > index eedfa8e9f077..8d20122ba0a8 100644
> > --- a/drivers/irqchip/irq-gic-v3.c
> > +++ b/drivers/irqchip/irq-gic-v3.c
> > @@ -78,6 +78,13 @@ static DEFINE_STATIC_KEY_TRUE(supports_deactivate_key);
> >  #define GIC_LINE_NR  min(GICD_TYPER_SPIS(gic_data.rdists.gicd_typer), 1020U)
> >  #define GIC_ESPI_NR  GICD_TYPER_ESPIS(gic_data.rdists.gicd_typer)
> >
> > +/*
> > + * There are 16 SGIs, though we only actually use 8 in Linux. The other 8 SGIs
> > + * are potentially stolen by the secure side. Some code, especially code dealing
> > + * with hwirq IDs, is simplified by accounting for all 16.
> > + */
> > +#define SGI_NR               16
> > +
> >  /*
> >   * The behaviours of RPR and PMR registers differ depending on the value of
> >   * SCR_EL3.FIQ, and the behaviour of non-secure priority registers of the
> > @@ -125,8 +132,8 @@ EXPORT_SYMBOL(gic_nonsecure_priorities);
> >               __priority;                                             \
> >       })
> >
> > -/* ppi_nmi_refs[n] == number of cpus having ppi[n + 16] set as NMI */
> > -static refcount_t *ppi_nmi_refs;
> > +/* rdist_nmi_refs[n] == number of cpus having the rdist interrupt n set as NMI */
> > +static refcount_t *rdist_nmi_refs;
> >
> >  static struct gic_kvm_info gic_v3_kvm_info __initdata;
> >  static DEFINE_PER_CPU(bool, has_rss);
> > @@ -519,9 +526,22 @@ static u32 __gic_get_ppi_index(irq_hw_number_t hwirq)
> >       }
> >  }
> >
> > -static u32 gic_get_ppi_index(struct irq_data *d)
> > +static u32 __gic_get_rdist_idx(irq_hw_number_t hwirq)
> > +{
> > +     switch (__get_intid_range(hwirq)) {
> > +     case SGI_RANGE:
> > +     case PPI_RANGE:
> > +             return hwirq;
> > +     case EPPI_RANGE:
> > +             return hwirq - EPPI_BASE_INTID + 32;
> > +     default:
> > +             unreachable();
> > +     }
> > +}
> > +
> > +static u32 gic_get_rdist_idx(struct irq_data *d)
> >  {
> > -     return __gic_get_ppi_index(d->hwirq);
> > +     return __gic_get_rdist_idx(d->hwirq);
> >  }
>
> Nit: It would be nicer to call this gic_get_rdist_index() to match
> gic_get_ppi_index(); likewise with __gic_get_rdist_index().
>
> That's my fault given I suggested the gic_get_rdist_idx() name in:
>
>   https://lore.kernel.org/linux-arm-kernel/ZNC-YRQopO0PaIIo@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>
> ... so sorry about that!

Yeah, I kept the name you suggested even though it seemed a little
inconsistent. I'll happily send a v13 with that fixed up, though I'll
probably wait a little bit just to avoid spamming new versions too
quickly. It's not like the patches can land in the middle of the merge
window anyway.

Unless someone says otherwise, I guess this series is in good shape to
land then. Does anyone have any plans for the details of how to land
it? I guess this would be something that Marc, Catalin and Will would
need to hash out since the first patch would ideally go through a
different tree than the others.

-Doug