linux-kernel - Re: next-20250702 WARNING iommu io-pgtable-arm.c at arm_lpae_map_pages qcom_iommu

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Message-Id: <ee234cd8-63dd-41fc-9a5f-94ffca21e2a1@app.fastmail.com>
Date: Wed, 09 Jul 2025 18:50:02 +0200
From: "Arnd Bergmann" <arnd@...db.de>
To: "Jason Gunthorpe" <jgg@...dia.com>,
 "Naresh Kamboju" <naresh.kamboju@...aro.org>
Cc: "open list" <linux-kernel@...r.kernel.org>, iommu@...ts.linux.dev,
 lkft-triage@...ts.linaro.org,
 "Linux Regressions" <regressions@...ts.linux.dev>,
 "Nicolin Chen" <nicolinc@...dia.com>,
 "Jean-Philippe Brucker" <jean-philippe@...aro.org>,
 "Anders Roxell" <anders.roxell@...aro.org>,
 "Benjamin Copeland" <benjamin.copeland@...aro.org>,
 "Dan Carpenter" <dan.carpenter@...aro.org>
Subject: Re: next-20250702 WARNING iommu io-pgtable-arm.c at arm_lpae_map_pages
 qcom_iommu_map

On Wed, Jul 9, 2025, at 18:26, Jason Gunthorpe wrote:
> On Wed, Jul 09, 2025 at 04:14:26PM +0530, Naresh Kamboju wrote:
>
> I believe the original text was a copy and pasto from an ARMv7s driver
> (ie the 32 bit ARM page table) which uses that unique combination of
> sizes. It is not a sane bitmap for HW with 64 bit page table support,
> there is never a 1M option for instance.
>
> So this removes 64k page support, which maybe didn't even work?

My guess would be that this bug is specific to this SoC running
in 32-bit mode. This is a rare exception and not really well
supported, as most 64-bit Arm chips require a 64-bit kernel, but
this one (along with Broadcom bcm283x) can do either.

When running a 32-bit kernel, there is definitely no support for
64KB pages in the CPU, unlike on arm64.

    Arnd