Messages in this thread | | | Date | Thu, 7 Sep 2023 13:57:42 +0100 | Subject | Re: [PATCH v3] cma: check for memory region overlapping | From | Robin Murphy <> |
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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;
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