Re: [PATCH 3/5] kexec_file: Honor the segment alignment for CMA allocations

From: Mike Rapoport <rppt@kernel.org>
To: gaohan@iscas.ac.cn
Cc: Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Bill Wendling <morbo@google.com>,
	Justin Stitt <justinstitt@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Baoquan He <baoquan.he@linux.dev>,
	Pasha Tatashin <pasha.tatashin@soleen.com>,
	Pratyush Yadav <pratyush@kernel.org>, Yao Zi <me@ziyao.cc>,
	Han Gao <rabenda.cn@gmail.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	llvm@lists.linux.dev, kexec@lists.infradead.org
Subject: Re: [PATCH 3/5] kexec_file: Honor the segment alignment for CMA allocations
Date: Tue, 3 Nov 2026 12:14:50 +0200	[thread overview]
Message-ID: <aum0GlBKTfZ6rvgL@kernel.org> (raw)
In-Reply-To: <20261023-riscv-kexec-cma-fixes-v1-3-825b90ea23c4@iscas.ac.cn>

On Fri, Oct 23, 2026 at 03:33:16PM +0800, Han Gao via B4 Relay wrote:
> From: Han Gao <gaohan@iscas.ac.cn>
> 
> dma_alloc_from_contiguous() limits the requested alignment to
> CONFIG_CMA_ALIGNMENT without reporting it. kexec_alloc_contig() can
> therefore place a segment at a less aligned address than buf_align. On
> RISC-V with 4 KiB pages, the default 1 MiB limit is below the 2 MiB
> kernel alignment, and the new kernel stops at the setup_vm() BUG_ON for
> a misaligned physical address.
> 
> Release such a block and fall back to the regular memory hole search,
> which honors the alignment.
> 
> Fixes: 07d24902977e ("kexec: enable CMA based contiguous allocation")
> Signed-off-by: Han Gao <gaohan@iscas.ac.cn>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> ---
>  kernel/kexec_file.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 59fb9d71e9d8..6ce10e01414e 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -690,6 +690,13 @@ static int kexec_alloc_contig(struct kexec_buf *kbuf)
>  
>  	mem = page_to_boot_pfn(p) << PAGE_SHIFT;
>  
> +	/* dma_alloc_from_contiguous() caps the alignment at CONFIG_CMA_ALIGNMENT. */
> +	if (!IS_ALIGNED(mem, kbuf->buf_align)) {
> +		pr_debug("CMA block 0x%lx is not aligned to 0x%lx\n", mem, kbuf->buf_align);
> +		dma_release_from_contiguous(NULL, p, nr_pages);
> +		return -EINVAL;
> +	}
> +
>  	if (kimage_is_destination_range(kbuf->image, mem, mem + kbuf->memsz)) {
>  		/* Our region is already in use by a statically defined one. Bail out. */
>  		pr_debug("CMA overlaps existing mem: 0x%lx+0x%lx\n", mem, kbuf->memsz);
> 
> -- 
> 2.55.0
> 
> 

-- 
Sincerely yours,
Mike.

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