linux-kernel - Re: [PATCH 6/7] irqchip/gic-v3-its: Honor hypervisor enforced LPI range

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Date:   Fri, 22 Jun 2018 18:54:16 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Shanker Donthineni <shankerd@...eaurora.org>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Lei Zhang <zhang.lei@...fujitsu.com>,
        Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH 6/7] irqchip/gic-v3-its: Honor hypervisor enforced LPI range

Hi Shammer,

On Fri, 22 Jun 2018 17:31:40 +0100,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com> wrote:
> 
> Hi Marc,
> 
> > -----Original Message-----
> > From: Marc Zyngier [mailto:marc.zyngier@....com]
> > Sent: 20 June 2018 14:53
> > To: linux-kernel@...r.kernel.org
> > Cc: Thomas Gleixner <tglx@...utronix.de>; Ard Biesheuvel
> > <ard.biesheuvel@...aro.org>; Shanker Donthineni
> > <shankerd@...eaurora.org>; Shameerali Kolothum Thodi
> > <shameerali.kolothum.thodi@...wei.com>; MaJun <majun258@...wei.com>;
> > Laurentiu Tudor <laurentiu.tudor@....com>; Lei Zhang
> > <zhang.lei@...fujitsu.com>
> > Subject: [PATCH 6/7] irqchip/gic-v3-its: Honor hypervisor enforced LPI range
> > 
> > A recent extension to the GIC architecture allows a hypervisor to
> > arbitrarily reduce the number of LPIs available to a guest, no
> > matter what the GIC says about the valid range of IntIDs.
> > 
> > Let's factor in this information when computing the number of
> > available LPIs
> 
> On our D05 board, this limits the lpis to 2 and results in MSI irq
> alloc fails:
> 
> [    0.000000] ITS: Using hypervisor restricted LPI range [2]
> ....
> [   10.543889] ixgbe 000a:11:00.1: Failed to allocate MSI interrupt, falling back to legacy. Error: -12
>  
> > Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> > ---
> >  drivers/irqchip/irq-gic-v3-its.c   | 9 +++++++++
> >  include/linux/irqchip/arm-gic-v3.h | 1 +
> >  2 files changed, 10 insertions(+)
> > 
> > diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> > index 8c7e8c235faf..903ca1c19553 100644
> > --- a/drivers/irqchip/irq-gic-v3-its.c
> > +++ b/drivers/irqchip/irq-gic-v3-its.c
> > @@ -1525,8 +1525,17 @@ static int free_lpi_range(u32 base, u32 nr_lpis)
> >  static int __init its_lpi_init(u32 id_bits)
> >  {
> >  	u32 lpis = (1UL << id_bits) - 8192;
> > +	u32 numlpis;
> >  	int err;
> > 
> > +	numlpis = 1UL << GICD_TYPER_NUM_LPIS(gic_rdists->gicd_typer);
> > +
> > +	if (numlpis > 1 && !WARN_ON(numlpis > lpis)) {
> > +		lpis = numlpis;
> > +		pr_info("ITS: Using hypervisor restricted LPI range [%u]\n",
> > +			lpis);
> > +	}
> 
> I don't have the GICv3 extension doc, but did you intent to check for,
> 
>  if (numlpis > 2 && !WARN_ON(numlpis > lpis)) {
> 
> as it looks like D05 returns 0 for bits 11-15 and that makes numlpis=2.

Absolutely. This really is a silly bug, thanks for catching that one.
I've pushed out an update on my irq/lpi-allocator branch.

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.