drm/amdkfd: Handle lack of READ permissions in SVM mapping

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[ Upstream commit 0ed704d058 ]

HMM assumes that pages have READ permissions by default. Inside
svm_range_validate_and_map, we add READ permissions then add WRITE
permissions if the VMA isn't read-only. This will conflict with regions
that only have PROT_WRITE or have PROT_NONE. When that happens,
svm_range_restore_work will continue to retry, silently, giving the
impression of a hang if pr_debug isn't enabled to show the retries..

If pages don't have READ permissions, simply unmap them and continue. If
they weren't mapped in the first place, this would be a no-op. Since x86
doesn't support write-only, and PROT_NONE doesn't allow reads or writes
anyways, this will allow the svm range validation to continue without
getting stuck in a loop forever on mappings we can't use with HMM.

Signed-off-by: Kent Russell <kent.russell@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

...

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Kent Russell 2025-07-21 14:06:36 -04:00 • committed by Greg Kroah-Hartman

parent 273d1ea12e

commit 790c701078

1 changed files with 23 additions and 0 deletions

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drivers/gpu/drm/amd/amdkfd/kfd_svm.c

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