On Tue, Jan 17, 2023 at 11:49:20AM +0800, Baoquan He wrote:
> On arm64, reservation for 'crashkernel=xM,high' is taken by searching for
> suitable memory region up down. If the 'xM' of crashkernel high memory
> is reserved from high memory successfully, it will try to reserve
> crashkernel low memory later accoringly. Otherwise, it will try to search
> low memory area for the 'xM' suitable region.
>
> While we observed an unexpected case where a reserved region crosses the
> high and low meomry boundary. E.g on a system with 4G as low memory end,
> user added the kernel parameters like: 'crashkernel=512M,high', it could
> finally have [4G-126M, 4G+386M], [1G, 1G+128M] regions in running kernel.
> This looks very strange because we have two low memory regions
> [4G-126M, 4G] and [1G, 1G+128M]. Much explanation need be given to tell
> why that happened.
>
> Here, for crashkernel=xM,high, search the high memory for the suitable
> region above the high and low memory boundary. If failed, try reserving
> the suitable region below the boundary. Like this, the crashkernel high
> region will only exist in high memory, and crashkernel low region only
> exists in low memory. The reservation behaviour for crashkernel=,high is
> clearer and simpler.
>
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> ---
> arch/arm64/mm/init.c | 30 +++++++++++++++++++++++-------
> 1 file changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 58a0bb2c17f1..26a05af2bfa8 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -127,12 +127,13 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
> */
> static void __init reserve_crashkernel(void)
> {
> - unsigned long long crash_base, crash_size;
> - unsigned long long crash_low_size = 0;
> + unsigned long long crash_base, crash_size, search_base;
> unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
> + unsigned long long crash_low_size = 0;
> char *cmdline = boot_command_line;
> - int ret;
> bool fixed_base = false;
> + bool high = false;
> + int ret;
>
> if (!IS_ENABLED(CONFIG_KEXEC_CORE))
> return;
> @@ -155,7 +156,9 @@ static void __init reserve_crashkernel(void)
> else if (ret)
> return;
>
> + search_base = CRASH_ADDR_LOW_MAX;
> crash_max = CRASH_ADDR_HIGH_MAX;
> + high = true;
> } else if (ret || !crash_size) {
> /* The specified value is invalid */
> return;
> @@ -166,31 +169,44 @@ static void __init reserve_crashkernel(void)
> /* User specifies base address explicitly. */
> if (crash_base) {
> fixed_base = true;
> + search_base = crash_base;
> crash_max = crash_base + crash_size;
> }
>
> retry:
> crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
> - crash_base, crash_max);
> + search_base, crash_max);
> if (!crash_base) {
> + if (fixed_base) {
> + pr_warn("cannot reserve crashkernel region [0x%llx-0x%llx]\n",
> + search_base, crash_max);
> + return;
> + }
> +
> /*
> * If the first attempt was for low memory, fall back to
> * high memory, the minimum required low memory will be
> * reserved later.
> */
> - if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
> + if (!high && crash_max == CRASH_ADDR_LOW_MAX) {
> crash_max = CRASH_ADDR_HIGH_MAX;
> + search_base = CRASH_ADDR_LOW_MAX;
> crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> goto retry;
> }
>
> + if (high && (crash_max == CRASH_ADDR_HIGH_MAX)) {
nit: unnecessary (and inconsistent with code just above) parentheses.
> + crash_max = CRASH_ADDR_LOW_MAX;
> + search_base = 0;
> + goto retry;
> + }
> pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
> crash_size);
> return;
> }
>
> - if ((crash_base > CRASH_ADDR_LOW_MAX - crash_low_size) &&
> - crash_low_size && reserve_crashkernel_low(crash_low_size)) {
> + if ((crash_base >= CRASH_ADDR_LOW_MAX) && crash_low_size &&
> + reserve_crashkernel_low(crash_low_size)) {
> memblock_phys_free(crash_base, crash_size);
> return;
> }
> --
> 2.34.1
>
>
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