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

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Message-ID: <20250709162609.GD1599700@nvidia.com>
Date: Wed, 9 Jul 2025 13:26:09 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: 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>,
	Ben Copeland <benjamin.copeland@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	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 09, 2025 at 04:14:26PM +0530, Naresh Kamboju wrote:
> I have tested this patch on top of Linux next-20250702 tag,
> and found kernel warning,

Oh, yeah, I guess that hacky fix is not going to work.

Then this is probably good enough (against linux-next):

--- a/drivers/iommu/arm/arm-smmu/qcom_iommu.c
+++ b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
@@ -335,7 +335,7 @@ static struct iommu_domain *qcom_iommu_domain_alloc_paging(struct device *dev)

        mutex_init(&qcom_domain->init_mutex);
        spin_lock_init(&qcom_domain->pgtbl_lock);
-       qcom_domain->domain.pgsize_bitmap = SZ_4K | SZ_64K | SZ_1M | SZ_16M;
+       qcom_domain->domain.pgsize_bitmap = SZ_4K | SZ_2M;

        return &qcom_domain->domain;
 }

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?

I also prepared a proper rework that puts the pgtable allocation into
the qcom_iommu_domain_alloc_paging(). I've attached it, but it is
involved enough it probably breaks something else. However if you
want to test it maybe we can progress it too.

Thanks,
Jason

View attachment "0001-iommu-qcom-Allocate-the-iopgtbl-inside-qcom_iommu_do.patch" of type "text/x-diff" (8839 bytes)