lkml.org 
[lkml]   [2023]   [Sep]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH v3] cma: check for memory region overlapping
From
On 26/07/2023 3:28 pm, Binglei Wang wrote:
> From: Binglei Wang <l3b2w1@gmail.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@gmail.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;

\
 
 \ /
  Last update: 2023-09-07 20:23    [W:0.107 / U:0.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site