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

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

[Sasha Levin]

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 <stable@vger.kernel.org>.

Thanks,
Sasha

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

From 2172d6ebac9372eb01fe4505a53e18cb061e103b Mon Sep 17 00:00:00 2001
From: Huacai Chen <chenhuacai@loongson.cn>
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: stable@vger.kernel.org
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
---
 arch/loongarch/kernel/setup.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
index 20cb6f3064568..2b260d15b2e25 100644
--- a/arch/loongarch/kernel/setup.c
+++ b/arch/loongarch/kernel/setup.c
@@ -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

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

[Huacai Chen]

Hi, Sasha,

On Sun, Mar 1, 2026 at 9:37 AM Sasha Levin <sashal@kernel.org> wrote:
>
> 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 <stable@vger.kernel.org>.
I'm very confused because it can be applied and already here:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git/tree/queue-6.6

Huacai

>
> Thanks,
> Sasha
>
> ------------------ original commit in Linus's tree ------------------
>
> From 2172d6ebac9372eb01fe4505a53e18cb061e103b Mon Sep 17 00:00:00 2001
> From: Huacai Chen <chenhuacai@loongson.cn>
> 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: stable@vger.kernel.org
> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> ---
>  arch/loongarch/kernel/setup.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> index 20cb6f3064568..2b260d15b2e25 100644
> --- a/arch/loongarch/kernel/setup.c
> +++ b/arch/loongarch/kernel/setup.c
> @@ -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
>
>
>
>