On Mon, 31 May 2021 15:29:55 +0300
Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
>
> Commit 4e042af463f8 ("s390/kexec: fix crash on resize of reserved memory")
> added a comment that says "crash kernel resource should not be part of the
> System RAM resource" but never explained why. As it looks from the code in
> the kernel and in kexec there is no actual reason for that.
Still testing, but so far everything works fine.
>
> Keeping crashk_res inline with other resources makes code simpler and
> cleaner, and allows future consolidation of the resources setup across
> several architectures.
>
> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> ---
> arch/s390/kernel/setup.c | 21 +++++----------------
> 1 file changed, 5 insertions(+), 16 deletions(-)
>
> diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
> index 5aab59ad5688..30430e7c1b03 100644
> --- a/arch/s390/kernel/setup.c
> +++ b/arch/s390/kernel/setup.c
> @@ -500,6 +500,9 @@ static struct resource __initdata *standard_resources[] = {
> &code_resource,
> &data_resource,
> &bss_resource,
> +#ifdef CONFIG_CRASH_DUMP
> + &crashk_res,
> +#endif
> };
>
> static void __init setup_resources(void)
> @@ -535,7 +538,7 @@ static void __init setup_resources(void)
>
> for (j = 0; j < ARRAY_SIZE(standard_resources); j++) {
> std_res = standard_resources[j];
> - if (std_res->start < res->start ||
> + if (!std_res->end || std_res->start < res->start ||
> std_res->start > res->end)
> continue;
> if (std_res->end > res->end) {
Why is this extra check for !std_res->end added here? I assume it
might be needed later, after you moved this to common code, but I
cannot see how any of the other patches in this series would require
that.
> @@ -552,20 +555,6 @@ static void __init setup_resources(void)
> }
> }
> }
> -#ifdef CONFIG_CRASH_DUMP
> - /*
> - * Re-add removed crash kernel memory as reserved memory. This makes
> - * sure it will be mapped with the identity mapping and struct pages
> - * will be created, so it can be resized later on.
> - * However add it later since the crash kernel resource should not be
> - * part of the System RAM resource.
> - */
> - if (crashk_res.end) {
> - memblock_add_node(crashk_res.start, resource_size(&crashk_res), 0);
> - memblock_reserve(crashk_res.start, resource_size(&crashk_res));
> - insert_resource(&iomem_resource, &crashk_res);
> - }
> -#endif
> }
>
> static void __init setup_ident_map_size(void)
> @@ -733,7 +722,7 @@ static void __init reserve_crashkernel(void)
> diag10_range(PFN_DOWN(crash_base), PFN_DOWN(crash_size));
> crashk_res.start = crash_base;
> crashk_res.end = crash_base + crash_size - 1;
> - memblock_remove(crash_base, crash_size);
> + memblock_reserve(crash_base, crash_size);
> pr_info("Reserving %lluMB of memory at %lluMB "
> "for crashkernel (System RAM: %luMB)\n",
> crash_size >> 20, crash_base >> 20,
Other architectures check the return value of memblock_reserve() at
this point, and exit crashkernel reservation if it fails. IIUC, the
only reason why memblock_reserve() could fail would be the same reason
why also memblock_remove() could fail, i.e. that memblock_double_array()
would fail. And since we also do not check that at the moment, your
patch would probably not (additionally) break anything.
Still, this might be something for an add-on patch (for us). Do you
happen to know how likely it would be that memblock_remove/reserve()
could fail at this point?
