linux-kernel - Re: [PATCH 1/1] drm/amdkfd: fix build error with AMD_IOMMU

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Date:   Tue, 9 Mar 2021 09:58:37 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Felix Kuehling <Felix.Kuehling@....com>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        "open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/1] drm/amdkfd: fix build error with AMD_IOMMU_V2=m

On Tue, Mar 9, 2021 at 4:23 AM Felix Kuehling <Felix.Kuehling@....com> wrote:
>
> Using 'imply AMD_IOMMU_V2' does not guarantee that the driver can link
> against the exported functions. If the GPU driver is built-in but the
> IOMMU driver is a loadable module, the kfd_iommu.c file is indeed
> built but does not work:
>
> x86_64-linux-ld: drivers/gpu/drm/amd/amdkfd/kfd_iommu.o: in function `kfd_iommu_bind_process_to_device':
> kfd_iommu.c:(.text+0x516): undefined reference to `amd_iommu_bind_pasid'
> x86_64-linux-ld: drivers/gpu/drm/amd/amdkfd/kfd_iommu.o: in function `kfd_iommu_unbind_process':
> kfd_iommu.c:(.text+0x691): undefined reference to `amd_iommu_unbind_pasid'
> x86_64-linux-ld: drivers/gpu/drm/amd/amdkfd/kfd_iommu.o: in function `kfd_iommu_suspend':
> kfd_iommu.c:(.text+0x966): undefined reference to `amd_iommu_set_invalidate_ctx_cb'
> x86_64-linux-ld: kfd_iommu.c:(.text+0x97f): undefined reference to `amd_iommu_set_invalid_ppr_cb'
> x86_64-linux-ld: kfd_iommu.c:(.text+0x9a4): undefined reference to `amd_iommu_free_device'
> x86_64-linux-ld: drivers/gpu/drm/amd/amdkfd/kfd_iommu.o: in function `kfd_iommu_resume':
> kfd_iommu.c:(.text+0xa9a): undefined reference to `amd_iommu_init_device'
> x86_64-linux-ld: kfd_iommu.c:(.text+0xadc): undefined reference to `amd_iommu_set_invalidate_ctx_cb'
> x86_64-linux-ld: kfd_iommu.c:(.text+0xaff): undefined reference to `amd_iommu_set_invalid_ppr_cb'
> x86_64-linux-ld: kfd_iommu.c:(.text+0xc72): undefined reference to `amd_iommu_bind_pasid'
> x86_64-linux-ld: kfd_iommu.c:(.text+0xe08): undefined reference to `amd_iommu_set_invalidate_ctx_cb'
> x86_64-linux-ld: kfd_iommu.c:(.text+0xe26): undefined reference to `amd_iommu_set_invalid_ppr_cb'
> x86_64-linux-ld: kfd_iommu.c:(.text+0xe42): undefined reference to `amd_iommu_free_device'
>
> Use IS_REACHABLE to only build IOMMU-V2 support if the amd_iommu symbols
> are reachable by the amdkfd driver. Output a warning if they are not,
> because that may not be what the user was expecting.

This would fix the compile-time failure, but it still fails my CI
because you introduce
a compile-time warning. Can you change it into a runtime warning instead?

Neither type of warning is likely to actually reach the person trying
to debug the
problem, so you still end up with machines that don't do what they should,
but I can live with the runtime warning as long as the build doesn't break.

I think the proper fix would be to not rely on custom hooks into a particular
IOMMU driver, but to instead ensure that the amdgpu driver can do everything
it needs through the regular linux/iommu.h interfaces. I realize this
is more work,
but I wonder if you've tried that, and why it didn't work out.

       Arnd