linux-kernel - Re: [PATCH v3] iommu/amd: Add support for hw

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Message-ID: <20250902115722.GD186519@nvidia.com>
Date: Tue, 2 Sep 2025 08:57:22 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc: nicolinc@...dia.com, linux-kernel@...r.kernel.org, robin.murphy@....com,
	will@...nel.org, joro@...tes.org, kevin.tian@...el.com,
	jsnitsel@...hat.com, vasant.hegde@....com, iommu@...ts.linux.dev,
	santosh.shukla@....com, sairaj.arunkodilkar@....com,
	jon.grimm@....com, prashanthpra@...gle.com, wvw@...gle.com,
	wnliu@...gle.com, gptran@...gle.com, kpsingh@...gle.com
Subject: Re: [PATCH v3] iommu/amd: Add support for hw_info for iommu
 capability query

On Wed, Aug 27, 2025 at 04:23:09PM +0000, Suravee Suthikulpanit wrote:
> AMD IOMMU Extended Feature (EFR) and Extended Feature 2 (EFR2) registers
> specify features supported by each IOMMU hardware instance.
> The IOMMU driver checks each feature-specific bits before enabling
> each feature at run time.
> 
> For IOMMUFD, the hypervisor passes the raw value of amd_iommu_efr and
> amd_iommu_efr2 to VMM via iommufd IOMMU_DEVICE_GET_HW_INFO ioctl.
> 
> Reviewed-by: Nicolin Chen <nicolinc@...dia.com>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>

Was there a reason this is not part of the other series?

> +obj-y += iommu.o init.o quirks.o io_pgtable.o io_pgtable_v2.o ppr.o pasid.o iommufd.o

Part of the point of another file is to not compile it when !CONFIG_IOMMUFD

So you should change the makefile and add some header magic:

#if IS_ENABLED(CONFIG_IOMMUFD)
void *amd_iommufd_hw_info(struct device *dev, u32 *length, u32 *type);
#else
#define amd_iommufd_hw_info NULL
#endif

> +/**
> + * struct iommu_hw_info_amd - AMD IOMMU device info
> + *
> + * @efr : Value of AMD IOMMU Extended Feature Register (EFR) reported by hardware
> + * @efr2: Value of AMD IOMMU Extended Feature 2 Register (EFR2) reported by hardware
> + *
> + * Please See description of these registers in the following sections of
> + * the AMD I/O Virtualization Technology (IOMMU) Specification.
> + * (https://docs.amd.com/v/u/en-US/48882_3.10_PUB)
> + *
> + * - MMIO Offset 0030h IOMMU Extended Feature Register
> + * - MMIO Offset 01A0h IOMMU Extended Feature 2 Register
> + */

It would be good to elaborate on the bits like ARM does for
iommu_hw_info_arm_smmuv3 and where some of the bits should come from
in other places in the API.

Jason