drm/gpusvm: keep a single DMA mapping inline for THP

drm_gpusvm_get_pages() sizes the dma_addr array for one drm_pagemap_addr
per page, but the mapping loop advances by page order, so a range backed
by one huge page needs a single entry. For a 2 MiB THP that is an 8 KiB
array holding 16 bytes of address.

Union that entry with the array pointer, discriminated by a new
inline_dma_mapping flag. When drm_gpusvm_dma_map_pages() ends up with one
entry it stores it inline and frees the array, after the last error
unwind, which still walks the array form. An unchecked dma_addr read is
now type confusion rather than a compile error, so reads go through the
new drm_gpusvm_pages_first_dma() accessor, including the two
xe_pt_stage_bind() paths.

Only get_pages() and the free path write the union, never the notifier,
and both run under the driver lock that every address reader already
holds. The unlocked short circuit in drm_gpusvm_pages_valid_unlocked()
goes for the same reason: it cannot resolve the union, and every instance
it rejects has to be reset before the allocation loop reuses it.

Suggested-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Honglei Huang <honghuan@amd.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260905133142.3628027-6-honghuan@amd.com

0 files changed, 0 insertions, 0 deletions