linux-kernel - Re: [bug report] GICv4.1: vSGI remains pending across the guest reset

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Message-ID: <ZYB_RKR5CqlVS-lV@linux.dev>
Date: Mon, 18 Dec 2023 17:20:04 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Marc Zyngier <maz@...nel.org>
Cc: Kunkun Jiang <jiangkunkun@...wei.com>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
	kvmarm@...ts.linux.dev, open list <linux-kernel@...r.kernel.org>,
	"wanghaibin.wang@...wei.com" <wanghaibin.wang@...wei.com>
Subject: Re: [bug report] GICv4.1: vSGI remains pending across the guest reset

On Sun, Dec 17, 2023 at 06:52:55PM +0000, Marc Zyngier wrote:
> On Sun, 17 Dec 2023 17:34:38 +0000,
> Oliver Upton <oliver.upton@...ux.dev> wrote:
> > 
> > On Sun, Dec 17, 2023 at 05:33:16PM +0000, Oliver Upton wrote:
> > > On Sun, Dec 17, 2023 at 11:26:15AM +0000, Marc Zyngier wrote:
> > > 
> > > [...]
> > > 
> > > > But this has *nothing* to do with the guest. This is the *host*
> > > > userspace performing a write to the redistributor view, which has
> > > > different semantics. Which is why your earlier description made no
> > > > sense to me.
> > > > 
> > > > I think the problem is slightly larger than what you describe. A write
> > > > to ISPENDR0 should be propagated to the ITS for any values of the
> > > > latch, just like this happens on enabling HW-backed SGIs.
> > > > 
> > > > Can you please give this a go?
> > > 
> > > What do you think about using this as an opportunity for a bit of
> > > cleanup? It'd be nice unify the various MMIO and uaccess handlers for
> > > SPENDING + CPENDING while being careful about the arch_timer interrupt.
> 
> What is special about the timer interrupt?

Isn't that the case where we have a physical IRQ mapped and wind up
forwarding state to the physical GIC?

> Could be. But I'd rather have separate fixes from more invasive
> reworks.  Specially given that we have had multiple ugly bugs around
> this code in the past, which is why we ended up splitting userspace
> from guest accessors.

Fine by me. I had felt like a common helper w/ the user v. guest
exclusions is a bit easier to understand than diffing two very similar
functions, but it isn't a big deal.

Anyway, I'm happy with your fix. I'd like Kunkun to give it a go but
either way I can pick it up for 6.7.

-- 
Thanks,
Oliver