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Message-ID: <8c3fe8ce-4716-73f0-fb8a-ee982f212371@arm.com>
Date: Thu, 7 Sep 2023 13:57:42 +0100
From: Robin Murphy <robin.murphy@....com>
To: Binglei Wang <l3b2w1@...il.com>, hch@....de,
m.szyprowski@...sung.com
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] cma: check for memory region overlapping
On 26/07/2023 3:28 pm, Binglei Wang wrote:
> From: Binglei Wang <l3b2w1@...il.com>
>
> In the process of parsing the DTS, checks
> whether the memory region specified by the DTS CMA node area
> overlaps with the kernel text memory space reserved by memblock
> before calling early_init_fdt_scan_reserved_mem.
This description bears no relation to what the code actually does.
rmem_cma_setup() happens well after parsing the DTS, as it is that
initial parsing process in fdt_scan_reserved_mem() which *makes* the
memblock reservations in the first place. Thus, as the revert patch
demonstrates, by the time we get here to start *using* the reserved
region via fdt_init_reserved_mem(), it is always guaranteed to overlap a
reserved region because it trivially overlaps with itself.
Furthermore, even if the bootloader does stupidly load a non-relocatable
kernel into memory that it's described as reserved, the kernel text
pages should not be available for CMA to allocate from - and if they
were, that would be a far more fundamental bug elsewhere - so what is
the exact problem you're trying to solve here?
Thanks,
Robin.
> Maybe it's better to have some warning prompts printed.
>
> Signed-off-by: Binglei Wang <l3b2w1@...il.com>
> ---
>
> Notes:
> v3: fix compile error.
> v2: delete the logic code for handling return -EBUSY.
> v1: return -EBUSY when detect overlapping and handle the return case.
>
> kernel/dma/contiguous.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index 6ea80ae42..dc6d2af1e 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -410,6 +410,11 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
> return -EBUSY;
> }
>
> + if (memblock_is_region_reserved(rmem->base, rmem->size)) {
> + pr_info("Reserved memory: overlap with other memblock reserved region\n");
> + return -EBUSY;
> + }
> +
> if (!of_get_flat_dt_prop(node, "reusable", NULL) ||
> of_get_flat_dt_prop(node, "no-map", NULL))
> return -EINVAL;
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