linux-kernel - Re: [PATCH] irqchip/gic-v3-its: Correctly honor the RID remapping

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Message-ID: <ZpjCJLH3EEUELS2n@hovoldconsulting.com>
Date: Thu, 18 Jul 2024 09:20:04 +0200
From: Johan Hovold <johan@...nel.org>
To: Marc Zyngier <maz@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] irqchip/gic-v3-its: Correctly honor the RID remapping

On Wed, Jul 17, 2024 at 08:59:37PM +0100, Marc Zyngier wrote:
> Since 6adb35ff43a16 ("irqchip/gic-v3-its: Provide MSI parent for
> PCI/MSI[-X]"), the primary domain a PCI device allocates its interrupts
> from is the one that is directly attached to the device itself.
> 
> By virtue of being a PCI device, it has no OF node.
> 
> This domain is (through more layer than it is worth describing)
> passed to its_pci_msi_prepare(), which tries to compute the
> full RID that is presented to the ITS by the device. This is ultimately
> done by calling pci_msi_domain_get_msi_rid(), passing both the
> domain and the PCI device as arguments.
> 
> The baked-in assumption is that either the domain that is passed
> to pci_msi_domain_get_msi_rid() describes an interrupt controller
> with either an OF node or an entry in an ACPI IORT table.
> In our case, it is *neither*. This domain is does not represent

nit: stray "is"

> anything firmware-based, but just an allocation unit for the device.
> 
> As a result, we fail to provide the full RID (which requires inspecting
> the msi-map/msi-mask properties in the DT), and stick to the BDF,
> which isn't very useful.
> 
> Tragedy follows with a litany of devices that randomly die as
> they fail to see any MSI (because the RID is wrong) or fail to
> get an allocation (because they try to steal LPIs from their
> neighbour's pool).
> 
> This will happen on any system where a single ITS is shared by
> multiple root ports and end-points with overlapping BDF numbers,
> and has the topology described in the device-tree.  Simpler DT
> topologies will luckily work, and so will ACPI-based systems.
> 
> Solve it by pointing pci_msi_domain_get_msi_rid() at the *parent*
> domain, which is the ITS, resulting in a correct mapping and a
> restored happiness in my personal zoo.
> 
> Fixes: 6adb35ff43a16 ("irqchip/gic-v3-its: Provide MSI parent for PCI/MSI[-X]")
> Reported-by: Johan Hovold <johan@...nel.org>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>

This fixes the regression for the Qualcomm machines I ran into this
with:

Tested-by: Johan Hovold <johan+linaro@...nel.org>

Thanks!

Johan