linux-kernel - Re: [PATCH 2/3] irqchip/gic-v3: Detect LPI invalidation MMIO registers

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Message-ID: <87k0cny7lw.wl-maz@kernel.org>
Date:   Mon, 21 Mar 2022 09:31:39 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     linux-kernel@...r.kernel.org,
        Andre Przywara <andre.przywara@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH 2/3] irqchip/gic-v3: Detect LPI invalidation MMIO registers

On Thu, 17 Mar 2022 17:35:23 +0000,
Lorenzo Pieralisi <lorenzo.pieralisi@....com> wrote:
> 
> On Tue, Mar 15, 2022 at 04:50:33PM +0000, Marc Zyngier wrote:
> > Since GICv4.1, an implementation can offer the same MMIO-based
> > implementation as DirectLPI, only with an ITS. Given that this
> > can be hugely beneficial for workloads that are very LPI masking
> > heavy (although these workloads are admitedly a bit odd).
> > 
> > Interestingly, this is independent of RVPEI, which only *implies*
> > the functionnality.
> > 
> > So let's detect whether the implementation has GICR_CTLR.IR set,
> > and propagate this as DirectLPI to the ITS driver.
> > 
> > Signed-off-by: Marc Zyngier <maz@...nel.org>
> > ---
> >  drivers/irqchip/irq-gic-v3.c       | 15 +++++++++++----
> >  include/linux/irqchip/arm-gic-v3.h |  2 ++
> >  2 files changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> > index 736163d36b13..363bfe172033 100644
> > --- a/drivers/irqchip/irq-gic-v3.c
> > +++ b/drivers/irqchip/irq-gic-v3.c
> > @@ -918,7 +918,11 @@ static int gic_populate_rdist(void)
> >  static int __gic_update_rdist_properties(struct redist_region *region,
> >  					 void __iomem *ptr)
> >  {
> > -	u64 typer = gic_read_typer(ptr + GICR_TYPER);
> > +	u64 typer;
> > +	u32 ctlr;
> > +
> > +	typer = gic_read_typer(ptr + GICR_TYPER);
> > +	ctlr = readl_relaxed(ptr + GICR_CTLR);
> >  
> >  	/* Boot-time cleanip */
> >  	if ((typer & GICR_TYPER_VLPIS) && (typer & GICR_TYPER_RVPEID)) {
> > @@ -941,6 +945,7 @@ static int __gic_update_rdist_properties(struct redist_region *region,
> >  	/* RVPEID implies some form of DirectLPI, no matter what the doc says... :-/ */
> >  	gic_data.rdists.has_rvpeid &= !!(typer & GICR_TYPER_RVPEID);
> >  	gic_data.rdists.has_direct_lpi &= (!!(typer & GICR_TYPER_DirectLPIS) |
> > +					   !!(ctlr & GICR_CTLR_IR) |
> >  					   gic_data.rdists.has_rvpeid);
> >  	gic_data.rdists.has_vpend_valid_dirty &= !!(typer & GICR_TYPER_DIRTY);
> >  
> > @@ -962,7 +967,11 @@ static void gic_update_rdist_properties(void)
> >  	gic_iterate_rdists(__gic_update_rdist_properties);
> >  	if (WARN_ON(gic_data.ppi_nr == UINT_MAX))
> >  		gic_data.ppi_nr = 0;
> > -	pr_info("%d PPIs implemented\n", gic_data.ppi_nr);
> > +	pr_info("GICv3 features: %d PPIs, %s%s\n",
> > +		gic_data.ppi_nr,
> > +		gic_data.has_rss ? "RSS " : "",
> > +		gic_data.rdists.has_direct_lpi ? "DirectLPI " : "");
> 
> I understand GICR_CTLR.IR detection (which is v4.1 feature) - I don't

No, it is *also* a GICv3 feature. RVPEI implies IR, but IR is a
feature on its own (see my reply to Andre on the same subject).
Nothing restrict IR to a GICv4.1+ implementation, and KVM is about to
expose these registers to the GICv*3* guest.

> get why in this patch we are adding a GICv3 DirectLPI info dump (hunk
> above), it is probably nitpicking but the hunk above does not seem to
> belong in this patch - it is a separate print info refactoring or I am
> reading it wrongly.

It is indeed just refactoring the kernel messages so that we can see
that we enable DirectLPI for GICv3 as well. I honestly don't think
this deserves a separate patch.

Thanks,

	M.

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