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Date: Mon, 14 Feb 2022 15:53:31 +0800
From: "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To: Baoquan He <bhe@...hat.com>
CC: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
<x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
<linux-kernel@...r.kernel.org>, Dave Young <dyoung@...hat.com>,
Vivek Goyal <vgoyal@...hat.com>,
Eric Biederman <ebiederm@...ssion.com>,
<kexec@...ts.infradead.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
<linux-arm-kernel@...ts.infradead.org>,
Rob Herring <robh+dt@...nel.org>,
Frank Rowand <frowand.list@...il.com>,
<devicetree@...r.kernel.org>, "Jonathan Corbet" <corbet@....net>,
<linux-doc@...r.kernel.org>, Randy Dunlap <rdunlap@...radead.org>,
Feng Zhou <zhoufeng.zf@...edance.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>,
Chen Zhou <dingguo.cz@...group.com>,
"John Donnelly" <John.p.donnelly@...cle.com>,
Dave Kleikamp <dave.kleikamp@...cle.com>
Subject: Re: [PATCH v20 3/5] arm64: kdump: reimplement crashkernel=X
On 2022/2/14 11:52, Baoquan He wrote:
> On 01/24/22 at 04:47pm, Zhen Lei wrote:
> ......
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 6c653a2c7cff052..a5d43feac0d7d96 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -71,6 +71,30 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
>> #define CRASH_ADDR_LOW_MAX arm64_dma_phys_limit
>> #define CRASH_ADDR_HIGH_MAX MEMBLOCK_ALLOC_ACCESSIBLE
>>
>> +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%llx - 0x%llx (%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
>
> My another concern is the crashkernel=,low handling. In this patch, the
> code related to low memory is obscure. Wondering if we should make them
> explicit with a little redundant but very clear code flows. Saying this
> because the code must be very clear to you and reviewers, it may be
> harder for later code reader or anyone interested to understand.
>
> 1) crashkernel=X,high
> 2) crashkernel=X,high crashkernel=Y,low
> 3) crashkernel=X,high crashkernel=0,low
> 4) crashkernel=X,high crashkernel='messy code',low
> 5) crashkernel=X //fall back to high memory, low memory is required then.
>
> It could be me thinking about it too much. I made changes to your patch
> with a tuning, not sure if it's OK to you. Otherwise, this patchset
I think it's good.
> works very well for all above test cases, it's ripe to be merged for
> wider testing.
I will test it tomorrow. I've prepared a little more use cases than yours.
1) crashkernel=4G //high=4G, low=256M
2) crashkernel=4G crashkernel=512M,high crashkernel=512M,low //high=4G, low=256M, high and low are ignored
3) crashkernel=4G crashkernel=512M,high //high=4G, low=256M, high is ignored
4) crashkernel=4G crashkernel=512M,low //high=4G, low=256M, low is ignored
5) crashkernel=4G@...0000000 //high=0G, low=0M, cannot allocate, failed
6) crashkernel=512M //high=0G, low=512M
7) crashkernel=128M //high=0G, low=128M
8) crashkernel=512M@...e000000 //512M@...2M //high=0G, low=512M
9) crashkernel=4G,high //high=4G, low=256M
a) crashkernel=4G,high crashkernel=512M,low //high=4G, low=512M
b) crashkernel=512M,high crashkernel=128M,low //high=512M, low=128M
c) crashkernel=512M,low //high=0G, low=0M, invalid
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index a5d43feac0d7..671862c56d7d 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -94,7 +94,8 @@ static int __init reserve_crashkernel_low(unsigned long long low_size)
>
> return 0;
> }
> -
> +/*Words explaining why it's 256M*/
> +#define DEFAULT_CRASH_KERNEL_LOW_SIZE SZ_256M
> /*
> * reserve_crashkernel() - reserves memory for crash kernel
> *
> @@ -105,10 +106,10 @@ 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 = SZ_256M;
> + unsigned long long crash_low_size;
> unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
> int ret;
> - bool fixed_base;
> + bool fixed_base, high;
> char *cmdline = boot_command_line;
>
> /* crashkernel=X[@offset] */
> @@ -126,7 +127,10 @@ static void __init reserve_crashkernel(void)
> ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
> if (!ret)
> crash_low_size = low_size;
> + else
> + crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
>
> + high = true;
> crash_max = CRASH_ADDR_HIGH_MAX;
> }
>
> @@ -134,7 +138,7 @@ static void __init reserve_crashkernel(void)
> crash_size = PAGE_ALIGN(crash_size);
>
> /* User specifies base address explicitly. */
> - if (crash_base)
> + if (fixed_base)
> crash_max = crash_base + crash_size;
>
> retry:
> @@ -156,7 +160,10 @@ static void __init reserve_crashkernel(void)
> return;
> }
>
> - if (crash_base >= SZ_4G && reserve_crashkernel_low(crash_low_size)) {
> + if (crash_base >= SZ_4G && !high)
> + crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> +
> + if (reserve_crashkernel_low(crash_low_size)) {
> memblock_phys_free(crash_base, crash_size);
> return;
> }
It feels like {} may need to be added here so that it is in branch "if (crash_base >= SZ_4G)".
The case of "crashkernel=128M" will not fall back to high memory and does not need to reserve
low memory again.
>
>> *
>> @@ -81,29 +105,62 @@ 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_low_size = SZ_256M;
>> unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>> int ret;
>> + bool fixed_base;
>> + 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) {
>> + unsigned long long low_size;
>>
>> + /* crashkernel=X,high */
>> + ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
>> + if (ret || !crash_size)
>> + return;
>> +
>> + /* crashkernel=X,low */
>> + ret = parse_crashkernel_low(cmdline, 0, &low_size, &crash_base);
>> + if (!ret)
>> + crash_low_size = low_size;
>> +
>> + crash_max = CRASH_ADDR_HIGH_MAX;
>> + }
>> +
>> + fixed_base = !!crash_base;
>> crash_size = PAGE_ALIGN(crash_size);
>>
>> /* User specifies base address explicitly. */
>> if (crash_base)
>> 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.
>> + */
>> + 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 && 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);
>>
>> @@ -112,6 +169,9 @@ 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);
>> --
>> 2.25.1
>>
>
> .
>
--
Regards,
Zhen Lei
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