[PATCH v5 3/6] dma: swiotlb: Centralize minimal pool sizing
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From: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>
Date: 2026-09-21 06:37:43
Also in:
linux-arm-kernel, linux-iommu, linux-mips, linux-riscv, linux-s390, lkml, loongarch
Subsystem:
arm64 port (aarch64 architecture), dma mapping helpers, risc-v architecture, the rest · Maintainers:
Catalin Marinas, Will Deacon, Marek Szyprowski, Paul Walmsley, Palmer Dabbelt, Albert Ou, Linus Torvalds
Revision v5 of 4 in this series.
Revisions (4)
- v3 [diff vs current]
- v4 [diff vs current]
- v5 current
- v6 [diff vs current]
A default SWIOTLB pool used only for unaligned kmalloc bouncing can be smaller than one required for limited DMA addressing. Arm64 and RISC-V currently implement this sizing independently, using 1 MiB of SWIOTLB space per GiB of RAM. The SWIOTLB core now identifies this case with SWIOTLB_POOL_MINIMAL. Size that policy in swiotlb_adjust_pool_size() and remove the architecture-specific adjustments. Explicit swiotlb= sizing remains unchanged because swiotlb_adjust_size() preserves a user-configured size. Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org> --- arch/arm64/mm/init.c | 11 ----------- arch/riscv/mm/init.c | 4 ---- kernel/dma/swiotlb.c | 11 ++++++++++- 3 files changed, 10 insertions(+), 16 deletions(-)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 7d51fb5f5a71..95075b5c8207 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c@@ -340,17 +340,6 @@ void __init arch_mm_preinit(void) { unsigned int flags = SWIOTLB_VERBOSE; - if (max_pfn <= PFN_DOWN(arm64_dma_phys_limit)) { - /* - * If no bouncing needed for ZONE_DMA, reduce the swiotlb - * buffer for kmalloc() bouncing to 1MB per 1GB of RAM. - */ - unsigned long size = - DIV_ROUND_UP(memblock_phys_mem_size(), 1024); - - swiotlb_adjust_size(min(swiotlb_size_or_default(), size)); - } - if (max_pfn > PFN_DOWN(arm64_dma_phys_limit)) flags |= SWIOTLB_INIT_ADDRESSING_LIMIT;
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index e0e4c103d603..96856114b387 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c@@ -183,10 +183,6 @@ void __init arch_mm_preinit(void) * memory when DRAM starts above dma32_phys_limit. Allocate * ~1 MB per 1 GB of RAM. */ - unsigned long size = - DIV_ROUND_UP(memblock_phys_mem_size(), 1024); - swiotlb_adjust_size(min(swiotlb_size_or_default(), size)); - swiotlb = true; swiotlb_flags |= SWIOTLB_ANY; }
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 8f86deb25be2..f368a73f4ed0 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c@@ -483,9 +483,18 @@ static bool __init swiotlb_kmalloc_needs_bounce(void) static void __init swiotlb_adjust_pool_size(enum swiotlb_pool_policy policy) { + if (swiotlb_default_size_changed()) + return; + switch (policy) { - case SWIOTLB_POOL_MINIMAL: + case SWIOTLB_POOL_MINIMAL: { + unsigned long size; + + /* Use 1MB per 1GB of RAM for kmalloc() bouncing. */ + size = DIV_ROUND_UP(memblock_phys_mem_size(), 1024); + swiotlb_adjust_size(min(swiotlb_size_or_default(), size)); break; + } case SWIOTLB_POOL_CC_GUEST: break; case SWIOTLB_POOL_NONE:
--
2.43.0