Re: [PATCH v3 2/2] arm64: kdump: Support crashkernel=X fall back to reserve region above DMA zones

Catalin Marinas
2022-11-07T17:14:01Z

On Mon, Jul 11, 2022 at 05:03:19PM +0800, Zhen Lei wrote:
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 5390f361208ccf7..8539598f9e58b4d 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -138,6 +138,7 @@ static void __init reserve_crashkernel(void)
> unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
> char *cmdline = boot_command_line;
> int ret;
> + bool fixed_base;
>
> if (!IS_ENABLED(CONFIG_KEXEC_CORE))
> return;
> @@ -166,15 +167,28 @@ static void __init reserve_crashkernel(void)
> return;
> }
>
> + fixed_base = !!crash_base;
> crash_size = PAGE_ALIGN(crash_size);
>
> /* User specifies base address explicitly. */
> - if (crash_base)
> + if (fixed_base)
> crash_max = crash_base + crash_size;

Not a fan of '!!', it is converted automatically. If you don't like the
conversion, just initialise fixed_base to false and here:

if (crash_base) {
fixed_base = true;
crash_max = crash_base + crash_size;
}

> +retry:
> crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
> crash_base, crash_max);
> if (!crash_base) {
> + /*
> + * Attempt to fully allocate low memory failed, fall back
> + * to high memory, the minimum required low memory will be
> + * reserved later.
> + */

I'm not sure this comment makes sense. If !crash_base, it doesn't mean
the kernel failed to fully allocate low memory. crash_max here could be
CRASH_ADDR_HIGH_MAX if crashkerne=X,high was specified. Maybe says
something like "If the first attempt was for low memory, fall back to
high ..."

> + if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
> + crash_max = CRASH_ADDR_HIGH_MAX;
> + crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> + goto retry;
> + }

The retry logic looks fine, it only happens once as crash_max is
updated.

--
Catalin