Re: [PATCH] crash: keep crashkernel CMA pages reserved if activation fails

[Bradley Morgan <brads@mainlining.org>]

On 4 November 2026 14:56:00 GMT, Usama Arif <usama.arif@linux.dev> wrote:
>reserve_crashkernel_cma() adds each crashkernel CMA area to
>crashk_cma_ranges[] as soon as it is declared. If the area later fails
>activation, e.g. because movablecore= put the ZONE_MOVABLE boundary
>inside it, cma_activate_area() releases the pages to the buddy allocator
>as ordinary memory. The range is still handed to the crash kernel and
>excluded from the vmcore, so kernel data that lands there is overwritten
>by the crash kernel and missing from the dump.
>
>Mark the areas with cma_reserve_pages_on_error(), so that a failed
>activation leaves the pages reserved: lost to the first kernel, but safe
>for the crash kernel to use.
>
>Fixes: ab475510e042 ("kdump: implement reserve_crashkernel_cma")
>Signed-off-by: Usama Arif <usama.arif@linux.dev>
>---
> kernel/crash_reserve.c | 1 +
> 1 file changed, 1 insertion(+)
>
>diff --git a/kernel/crash_reserve.c b/kernel/crash_reserve.c
>index a03f0a4305a4e..a4b616ed49482 100644
>--- a/kernel/crash_reserve.c
>+++ b/kernel/crash_reserve.c
>@@ -498,6 +498,7 @@ void __init reserve_crashkernel_cma(unsigned long long cma_size)
> 			continue;
> 		}
> 
>+		cma_reserve_pages_on_error(res);

You do know that this will activate under every bitmap_zalloc() failure,
right? Is that accounted for?

> 		crashk_cma_ranges[crashk_cma_cnt].start = cma_get_base(res);
> 		crashk_cma_ranges[crashk_cma_cnt].end =
> 			crashk_cma_ranges[crashk_cma_cnt].start +
>

--- Thanks!