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SubjectRe: [PATCH 1/3] arm64: kdump: support reserving crashkernel above 4G
Hi,

On Wed, Apr 03, 2019 at 11:05:44AM +0800, Chen Zhou wrote:
> When crashkernel is reserved above 4G in memory, kernel should
> reserve some amount of low memory for swiotlb and some DMA buffers.
>
> Kernel would try to allocate at least 256M below 4G automatically
> as x86_64 if crashkernel is above 4G. Meanwhile, support
> crashkernel=X,[high,low] in arm64.
>
> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
> ---
> arch/arm64/kernel/setup.c | 3 ++
> arch/arm64/mm/init.c | 71 +++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 71 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 413d566..82cd9a0 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -243,6 +243,9 @@ static void __init request_standard_resources(void)
> request_resource(res, &kernel_data);
> #ifdef CONFIG_KEXEC_CORE
> /* Userspace will find "Crash kernel" region in /proc/iomem. */
> + if (crashk_low_res.end && crashk_low_res.start >= res->start &&
> + crashk_low_res.end <= res->end)
> + request_resource(res, &crashk_low_res);
> if (crashk_res.end && crashk_res.start >= res->start &&
> crashk_res.end <= res->end)
> request_resource(res, &crashk_res);
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 6bc1350..ceb2a25 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -64,6 +64,57 @@ EXPORT_SYMBOL(memstart_addr);
> phys_addr_t arm64_dma_phys_limit __ro_after_init;
>
> #ifdef CONFIG_KEXEC_CORE
> +static int __init reserve_crashkernel_low(void)
> +{
> + unsigned long long base, low_base = 0, low_size = 0;
> + unsigned long total_low_mem;
> + int ret;
> +
> + total_low_mem = memblock_mem_size(1UL << (32 - PAGE_SHIFT));
> +
> + /* crashkernel=Y,low */
> + ret = parse_crashkernel_low(boot_command_line, total_low_mem, &low_size, &base);
> + if (ret) {
> + /*
> + * two parts from lib/swiotlb.c:
> + * -swiotlb size: user-specified with swiotlb= or default.
> + *
> + * -swiotlb overflow buffer: now hardcoded to 32k. We round it
> + * to 8M for other buffers that may need to stay low too. Also
> + * make sure we allocate enough extra low memory so that we
> + * don't run out of DMA buffers for 32-bit devices.
> + */
> + low_size = max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20);
> + } else {
> + /* passed with crashkernel=0,low ? */
> + if (!low_size)
> + return 0;
> + }
> +
> + low_base = memblock_find_in_range(0, 1ULL << 32, low_size, SZ_2M);
> + if (!low_base) {
> + pr_err("Cannot reserve %ldMB crashkernel low memory, please try smaller size.\n",
> + (unsigned long)(low_size >> 20));
> + return -ENOMEM;
> + }
> +
> + ret = memblock_reserve(low_base, low_size);
> + if (ret) {
> + pr_err("%s: Error reserving crashkernel low memblock.\n", __func__);
> + return ret;
> + }
> +
> + pr_info("Reserving %ldMB of low memory at %ldMB for crashkernel (System RAM: %ldMB)\n",
> + (unsigned long)(low_size >> 20),
> + (unsigned long)(low_base >> 20),
> + (unsigned long)(total_low_mem >> 20));
> +
> + crashk_low_res.start = low_base;
> + crashk_low_res.end = low_base + low_size - 1;
> +
> + return 0;
> +}
> +
> /*
> * reserve_crashkernel() - reserves memory for crash kernel
> *
> @@ -74,19 +125,28 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
> static void __init reserve_crashkernel(void)
> {
> unsigned long long crash_base, crash_size;
> + bool high = false;
> int ret;
>
> ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> &crash_size, &crash_base);
> /* no crashkernel= or invalid value specified */
> - if (ret || !crash_size)
> - return;
> + if (ret || !crash_size) {
> + /* crashkernel=X,high */
> + ret = parse_crashkernel_high(boot_command_line, memblock_phys_mem_size(),
> + &crash_size, &crash_base);
> + if (ret || !crash_size)
> + return;
> + high = true;
> + }
>
> crash_size = PAGE_ALIGN(crash_size);
>
> if (crash_base == 0) {
> /* Current arm64 boot protocol requires 2MB alignment */
> - crash_base = memblock_find_in_range(0, ARCH_LOW_ADDRESS_LIMIT,
> + crash_base = memblock_find_in_range(0,
> + high ? memblock_end_of_DRAM()
> + : ARCH_LOW_ADDRESS_LIMIT,
> crash_size, SZ_2M);
> if (crash_base == 0) {
> pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
> @@ -112,6 +172,11 @@ static void __init reserve_crashkernel(void)
> }
> memblock_reserve(crash_base, crash_size);
>
> + if (crash_base >= SZ_4G && reserve_crashkernel_low()) {
> + memblock_free(crash_base, crash_size);
> + return;
> + }
> +

This very reminds what x86 does. Any chance some of the code can be reused
rather than duplicated?

> pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
> crash_base, crash_base + crash_size, crash_size >> 20);
>
> --
> 2.7.4
>

--
Sincerely yours,
Mike.

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