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    SubjectRe: [PATCH v21 3/5] arm64: kdump: reimplement crashkernel=X
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    On 2022/3/21 21:29, John Donnelly wrote:
    > On 2/26/22 9:07 PM, Zhen Lei wrote:
    >> From: Chen Zhou <chenzhou10@huawei.com>
    >>
    >> There are following issues in arm64 kdump:
    >> 1. We use crashkernel=X to reserve crashkernel below 4G, which
    >> will fail when there is no enough low memory.
    >
    >                         " Not enough "

    OK, thanks

    >> 2. If reserving crashkernel above 4G, in this case, crash dump
    >> kernel will boot failure because there is no low memory available
    >> for allocation.
    >
    >  We can't have a "boot failure". If the requested reservation
    >  can not be met,  the kdump  configuration is not setup.
    >>
    >> To solve these issues, change the behavior of crashkernel=X and
    >> introduce crashkernel=X,[high,low]. crashkernel=X tries low allocation
    >> in DMA zone, and fall back to high allocation if it fails.
    >> We can also use "crashkernel=X,high" to select a region above DMA zone,
    >> which also tries to allocate at least 256M in DMA zone automatically.
    >> "crashkernel=Y,low" can be used to allocate specified size low memory.
    >
    > Is there going to be documentation on what values certain Arm platforms are going to use this on ?

    There is no exact formula.

    >
    >>
    >> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
    >> Co-developed-by: Zhen Lei <thunder.leizhen@huawei.com>
    >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
    >> ---
    >>   arch/arm64/kernel/machine_kexec.c      |   9 ++-
    >>   arch/arm64/kernel/machine_kexec_file.c |  12 ++-
    >>   arch/arm64/mm/init.c                   | 106 +++++++++++++++++++++++--
    >>   3 files changed, 115 insertions(+), 12 deletions(-)
    >>
    >> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
    >> index e16b248699d5c3c..19c2d487cb08feb 100644
    >> --- a/arch/arm64/kernel/machine_kexec.c
    >> +++ b/arch/arm64/kernel/machine_kexec.c
    >> @@ -329,8 +329,13 @@ bool crash_is_nosave(unsigned long pfn)
    >>         /* in reserved memory? */
    >>       addr = __pfn_to_phys(pfn);
    >> -    if ((addr < crashk_res.start) || (crashk_res.end < addr))
    >> -        return false;
    >> +    if ((addr < crashk_res.start) || (crashk_res.end < addr)) {
    >> +        if (!crashk_low_res.end)
    >> +            return false;
    >> +
    >> +        if ((addr < crashk_low_res.start) || (crashk_low_res.end < addr))
    >> +            return false;
    >> +    }
    >>         if (!kexec_crash_image)
    >>           return true;
    >> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
    >> index 59c648d51848886..889951291cc0f9c 100644
    >> --- a/arch/arm64/kernel/machine_kexec_file.c
    >> +++ b/arch/arm64/kernel/machine_kexec_file.c
    >> @@ -65,10 +65,18 @@ static int prepare_elf_headers(void **addr, unsigned long *sz)
    >>         /* Exclude crashkernel region */
    >>       ret = crash_exclude_mem_range(cmem, crashk_res.start, crashk_res.end);
    >> +    if (ret)
    >> +        goto out;
    >> +
    >> +    if (crashk_low_res.end) {
    >> +        ret = crash_exclude_mem_range(cmem, crashk_low_res.start, crashk_low_res.end);
    >> +        if (ret)
    >> +            goto out;
    >> +    }
    >>   -    if (!ret)
    >> -        ret =  crash_prepare_elf64_headers(cmem, true, addr, sz);
    >> +    ret = crash_prepare_elf64_headers(cmem, true, addr, sz);
    >>   +out:
    >>       kfree(cmem);
    >>       return ret;
    >>   }
    >> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
    >> index 90f276d46b93bc6..30ae6638ff54c47 100644
    >> --- a/arch/arm64/mm/init.c
    >> +++ b/arch/arm64/mm/init.c
    >> @@ -65,6 +65,44 @@ EXPORT_SYMBOL(memstart_addr);
    >>   phys_addr_t arm64_dma_phys_limit __ro_after_init;
    >>     #ifdef CONFIG_KEXEC_CORE
    >> +/* Current arm64 boot protocol requires 2MB alignment */
    >> +#define CRASH_ALIGN            SZ_2M
    >> +
    >> +#define CRASH_ADDR_LOW_MAX        arm64_dma_phys_limit
    >> +#define CRASH_ADDR_HIGH_MAX        memblock.current_limit
    >> +
    >> +/*
    >> + * This is an empirical value in x86_64 and taken here directly. Please
    >> + * refer to the code comment in reserve_crashkernel_low() of x86_64 for more
    >> + * details.
    >> + */
    >> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE    \
    >> +    max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20)
    >> +
    >> +static int __init reserve_crashkernel_low(unsigned long long low_size)
    >> +{
    >> +    unsigned long long low_base;
    >> +
    >> +    /* passed with crashkernel=0,low ? */
    >> +    if (!low_size)
    >> +        return 0;
    >> +
    >> +    low_base = memblock_phys_alloc_range(low_size, CRASH_ALIGN, 0, CRASH_ADDR_LOW_MAX);
    >> +    if (!low_base) {
    >> +        pr_err("cannot allocate crashkernel low memory (size:0x%llx).\n", low_size);
    >> +        return -ENOMEM;
    >> +    }
    >> +
    >> +    pr_info("crashkernel low memory reserved: 0x%08llx - 0x%08llx (%lld MB)\n",
    >> +        low_base, low_base + low_size, low_size >> 20);
    >> +
    >> +    crashk_low_res.start = low_base;
    >> +    crashk_low_res.end   = low_base + low_size - 1;
    >> +    insert_resource(&iomem_resource, &crashk_low_res);
    >> +
    >> +    return 0;
    >> +}
    >> +
    >>   /*
    >>    * reserve_crashkernel() - reserves memory for crash kernel
    >>    *
    >> @@ -75,30 +113,79 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
    >>   static void __init reserve_crashkernel(void)
    >>   {
    >>       unsigned long long crash_base, crash_size;
    >> -    unsigned long long crash_max = arm64_dma_phys_limit;
    >> +    unsigned long long crash_low_size;
    >> +    unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
    >>       int ret;
    >> +    bool fixed_base, high = false;
    >> +    char *cmdline = boot_command_line;
    >>   -    ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
    >> +    /* crashkernel=X[@offset] */
    >> +    ret = parse_crashkernel(cmdline, 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(cmdline, 0, &crash_size, &crash_base);
    >> +        if (ret || !crash_size)
    >> +            return;
    >> +
    >> +        /* crashkernel=Y,low */
    >> +        ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
    >> +        if (ret == -ENOENT)
    >> +            /*
    >> +             * crashkernel=Y,low is not specified explicitly, use
    >> +             * default size automatically.
    >> +             */
    >> +            crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
    >> +        else if (ret)
    >> +            /* crashkernel=Y,low is specified but Y is invalid */
    >> +            return;
    >> +
    >> +        /* Mark crashkernel=X,high is specified */
    >> +        high = true;
    >> +        crash_max = CRASH_ADDR_HIGH_MAX;
    >> +    }
    >>   +    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;
    >>   -    /* Current arm64 boot protocol requires 2MB alignment */
    >> -    crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
    >> +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.
    >> +         */
    >> +        if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
    >> +            crash_max = CRASH_ADDR_HIGH_MAX;
    >> +            goto retry;
    >> +        }
    >> +
    >>           pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
    >>               crash_size);
    >>           return;
    >>       }
    >>   +    if (crash_base >= SZ_4G) {
    >> +        /*
    >> +         * For case crashkernel=X, low memory is not enough and fall
    >> +         * back to reserve specified size of memory above 4G, try to
    >> +         * allocate minimum required memory below 4G again.
    >> +         */
    >> +        if (!high)
    >> +            crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
    >> +
    >> +        if (reserve_crashkernel_low(crash_low_size)) {
    >> +            memblock_phys_free(crash_base, crash_size);
    >> +            return;
    >> +        }
    >> +    }
    >> +
    >>       pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
    >>           crash_base, crash_base + crash_size, crash_size >> 20);
    >>   @@ -107,6 +194,9 @@ static void __init reserve_crashkernel(void)
    >>        * map. Inform kmemleak so that it won't try to access it.
    >>        */
    >>       kmemleak_ignore_phys(crash_base);
    >> +    if (crashk_low_res.end)
    >> +        kmemleak_ignore_phys(crashk_low_res.start);
    >> +
    >>       crashk_res.start = crash_base;
    >>       crashk_res.end = crash_base + crash_size - 1;
    >>       insert_resource(&iomem_resource, &crashk_res);
    >
    > .
    >

    --
    Regards,
    Zhen Lei

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