linux-kernel - RE: [PATCH 1/7] vfio/pci: Disable auto-enable of exclusive INTx IRQ

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Date: Thu, 7 Mar 2024 08:28:45 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "eric.auger@...hat.com"
	<eric.auger@...hat.com>, "clg@...hat.com" <clg@...hat.com>, "Chatre,
 Reinette" <reinette.chatre@...el.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/7] vfio/pci: Disable auto-enable of exclusive INTx IRQ

> From: Alex Williamson <alex.williamson@...hat.com>
> Sent: Thursday, March 7, 2024 5:15 AM
> 
> Currently for devices requiring masking at the irqchip for INTx, ie.
> devices without DisINTx support, the IRQ is enabled in request_irq()
> and subsequently disabled as necessary to align with the masked status
> flag.  This presents a window where the interrupt could fire between
> these events, resulting in the IRQ incrementing the disable depth twice.

Can you elaborate the last point about disable depth?

> This would be unrecoverable for a user since the masked flag prevents
> nested enables through vfio.

What is 'nested enables'?

> 
> Instead, invert the logic using IRQF_NO_AUTOEN such that exclusive INTx
> is never auto-enabled, then unmask as required.
> 
> Fixes: 89e1f7d4c66d ("vfio: Add PCI device driver")
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>

But this patch looks good to me:

Reviewed-by: Kevin Tian <kevin.tian@...el.com>

with one nit...

> 
> +	/*
> +	 * Devices without DisINTx support require an exclusive interrupt,
> +	 * IRQ masking is performed at the IRQ chip.  The masked status is

"exclusive interrupt, with IRQ masking performed at..."