FAILED: Patch "LoongArch: Prefer top-down allocation after arch_mem_init()" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 2172d6ebac9372eb01fe4505a53e18cb061e103b Mon Sep 17 00:00:00 2001
From: Huacai Chen <[email protected]>
Date: Tue, 10 Feb 2026 19:31:13 +0800
Subject: [PATCH] LoongArch: Prefer top-down allocation after arch_mem_init()

Currently we use bottom-up allocation after sparse_init(), the reason is sparse_init() need a lot of memory, and bottom-up allocation may exhaust precious low memory (below 4GB). On the other hand, SWIOTLB and CMA need low memories for DMA32, so swiotlb_init() and dma_contiguous_reserve() need bottom-up allocation.

Since swiotlb_init() and dma_contiguous_reserve() are both called in arch_mem_init(), we no longer need bottom-up allocation after that. So we set the allocation policy to top-down at the end of arch_mem_init(), in order to avoid later memory allocations (such as KASAN) exhaust low memory.

This solve at least two problems:
1. Some buggy BIOSes use 0xfd000000~0xfe000000 for secondary CPUs, but didn't reserve this range, which causes smpboot failures.
2. Some DMA32 devices, such as Loongson-DRM and OHCI, cannot work with KASAN enabled.

Cc [email protected]

Signed-off-by Huacai Chen <[email protected]>

---
 arch/loongarch/kernel/setup.c | 1 +
 1 file changed, 1 insertion(+)

arch/loongarch/kernel/setup.c +1 -1

index 20cb6f3064568..2b260d15b2e25 100644
@@ -421,6 +421,7 @@ static void __init arch_mem_init(char **cmdline_p)
                                   PFN_UP(__pa_symbol(&__nosave_end)));
 
        memblock_dump_all();
+       memblock_set_bottom_up(false);
 
        early_memtest(PFN_PHYS(ARCH_PFN_OFFSET), PFN_PHYS(max_low_pfn));
 }
--

2.51.0