linux-kernel - Re: [PATCH] iommu/amd: Fix type of type parameter to amd_iommufd_hw

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Message-ID: <20260122233740.GA1589888@ziepe.ca>
Date: Thu, 22 Jan 2026 19:37:40 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Joerg Roedel <joro@...tes.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Vasant Hegde <vasant.hegde@....com>,
	Nicolin Chen <nicolinc@...dia.com>, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/amd: Fix type of type parameter to
 amd_iommufd_hw_info()

On Thu, Jan 22, 2026 at 02:42:38PM -0700, Nathan Chancellor wrote:
> When building with -Wincompatible-function-pointer-types-strict, a
> warning designed to catch kernel control flow integrity (kCFI) issues at
> build time, there is an instance around amd_iommufd_hw_info():
> 
>   drivers/iommu/amd/iommu.c:3141:13: error: incompatible function pointer types initializing 'void *(*)(struct device *, u32 *, enum iommu_hw_info_type *)' (aka 'void *(*)(struct device *, unsigned int *, enum iommu_hw_info_type *)') with an expression of type 'void *(struct device *, u32 *, u32 *)' (aka 'void *(struct device *, unsigned int *, unsigned int *)') [-Werror,-Wincompatible-function-pointer-types-strict]
>    3141 |         .hw_info = amd_iommufd_hw_info,
>         |                    ^~~~~~~~~~~~~~~~~~~
> 
> While 'u32 *' and 'enum iommu_hw_info_type *' are ABI compatible, hence
> no regular warning from -Wincompatible-function-pointer-types, the
> mismatch will trigger a kCFI violation when amd_iommufd_hw_info() is
> called indirectly.
> 
> Update the type parameter of amd_iommufd_hw_info() to be
> 'enum iommu_hw_info_type *' to match the prototype in
> 'struct iommu_ops', clearing up the warning and kCFI violation.
> 
> Fixes: 7d8b06ecc45b ("iommu/amd: Add support for hw_info for iommu capability query")
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  drivers/iommu/amd/iommufd.c | 2 +-
>  drivers/iommu/amd/iommufd.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com

Jason