linux-kernel - [PATCH v4 0/2] swiotlb: allocate padding slots if necessary

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Date: Mon, 25 Mar 2024 09:31:03 +0100
From: Petr Tesarik <petrtesarik@...weicloud.com>
To: Christoph Hellwig <hch@....de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Petr Tesarik <petr.tesarik1@...wei-partners.com>,
	Michael Kelley <mhklinux@...look.com>,
	Will Deacon <will@...nel.org>,
	linux-kernel@...r.kernel.org (open list),
	iommu@...ts.linux.dev (open list:DMA MAPPING HELPERS)
Cc: Roberto Sassu <roberto.sassu@...weicloud.com>,
	Petr Tesarik <petr@...arici.cz>
Subject: [PATCH v4 0/2] swiotlb: allocate padding slots if necessary

From: Petr Tesarik <petr.tesarik1@...wei-partners.com>

If the allocation alignment is bigger than IO_TLB_SIZE and min_align_mask
covers some bits in the original address between IO_TLB_SIZE and
alloc_align_mask, preserve these bits by allocating additional padding
slots before the actual swiotlb buffer.

Changes from v3
---------------
* Add a parameter to swiotlb_align_offset(), so it is not open-coded in
  swiotlb_tbl_map_single().
* Extend the description of swiotlb_align_offset() and convert it to the
  kernel-doc format.
* Use bit operations to calculate number of padding slots and the padding
  inside a slot. This matches all other such calculations in swiotlb.c.

Changes from v2
---------------
* Fix assignment of an uninitialized variable to pad_slots.
* Improve commit message wrt INVALID_PHYS_ADDR.

Changes from v1
---------------
* Rename padding to pad_slots.
* Set pad_slots only for the first allocated non-padding slot.
* Do not bother initializing orig_addr to INVALID_PHYS_ADDR.
* Change list and pad_slots to unsigned short to avoid growing
  struct io_tlb_slot on 32-bit targets.
* Add build-time check that list and pad_slots can hold the maximum
  allowed value of IO_TLB_SEGSIZE.


Petr Tesarik (2):
  swiotlb: extend buffer pre-padding to alloc_align_mask if necessary
  bug: introduce ASSERT_VAR_CAN_HOLD()

 include/linux/build_bug.h | 10 +++++++
 kernel/dma/swiotlb.c      | 61 ++++++++++++++++++++++++++++++---------
 2 files changed, 58 insertions(+), 13 deletions(-)

-- 
2.34.1