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Subject: Re: [PATCH 2/3] arm64: kdump: support more than one crash kernel
 regions
To:     Mike Rapoport <rppt@linux.ibm.com>
References: <20190403030546.23718-1-chenzhou10@huawei.com>
 <20190403030546.23718-3-chenzhou10@huawei.com>
 <20190403112929.GA7715@rapoport-lnx>
 <f98a5559-3659-fb35-3765-15861e70a796@huawei.com>
 <20190404144408.GA6433@rapoport-lnx>
 <783b8712-ddb1-a52b-81ee-0c6a216e5b7d@huawei.com>
CC:     <catalin.marinas@arm.com>, <will.deacon@arm.com>,
        <akpm@linux-foundation.org>, <ard.biesheuvel@linaro.org>,
        <takahiro.akashi@linaro.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <kexec@lists.infradead.org>,
        <linux-mm@kvack.org>, <wangkefeng.wang@huawei.com>
From:   Chen Zhou <chenzhou10@huawei.com>
Message-ID: <4b188535-c12d-e05b-9154-2c2d580f903b@huawei.com>
Date:   Fri, 5 Apr 2019 11:47:27 +0800
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Hi Mike,

On 2019/4/5 10:17, Chen Zhou wrote:
> Hi Mike,
> 
> On 2019/4/4 22:44, Mike Rapoport wrote:
>> Hi,
>>
>> On Wed, Apr 03, 2019 at 09:51:27PM +0800, Chen Zhou wrote:
>>> Hi Mike,
>>>
>>> On 2019/4/3 19:29, Mike Rapoport wrote:
>>>> On Wed, Apr 03, 2019 at 11:05:45AM +0800, Chen Zhou wrote:
>>>>> After commit (arm64: kdump: support reserving crashkernel above 4G),
>>>>> there may be two crash kernel regions, one is below 4G, the other is
>>>>> above 4G.
>>>>>
>>>>> Crash dump kernel reads more than one crash kernel regions via a dtb
>>>>> property under node /chosen,
>>>>> linux,usable-memory-range = <BASE1 SIZE1 [BASE2 SIZE2]>
>>>>>
>>>>> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
>>>>> ---
>>>>>  arch/arm64/mm/init.c     | 37 +++++++++++++++++++++++++------------
>>>>>  include/linux/memblock.h |  1 +
>>>>>  mm/memblock.c            | 40 ++++++++++++++++++++++++++++++++++++++++
>>>>>  3 files changed, 66 insertions(+), 12 deletions(-)
>>>>>
>>>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>>>> index ceb2a25..769c77a 100644
>>>>> --- a/arch/arm64/mm/init.c
>>>>> +++ b/arch/arm64/mm/init.c
>>>>> @@ -64,6 +64,8 @@ EXPORT_SYMBOL(memstart_addr);
>>>>>  phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>>>>  
>>>>>  #ifdef CONFIG_KEXEC_CORE
>>>>> +# define CRASH_MAX_USABLE_RANGES        2
>>>>> +
>>>>>  static int __init reserve_crashkernel_low(void)
>>>>>  {
>>>>>  	unsigned long long base, low_base = 0, low_size = 0;
>>>>> @@ -346,8 +348,8 @@ static int __init early_init_dt_scan_usablemem(unsigned long node,
>>>>>  		const char *uname, int depth, void *data)
>>>>>  {
>>>>>  	struct memblock_region *usablemem = data;
>>>>> -	const __be32 *reg;
>>>>> -	int len;
>>>>> +	const __be32 *reg, *endp;
>>>>> +	int len, nr = 0;
>>>>>  
>>>>>  	if (depth != 1 || strcmp(uname, "chosen") != 0)
>>>>>  		return 0;
>>>>> @@ -356,22 +358,33 @@ static int __init early_init_dt_scan_usablemem(unsigned long node,
>>>>>  	if (!reg || (len < (dt_root_addr_cells + dt_root_size_cells)))
>>>>>  		return 1;
>>>>>  
>>>>> -	usablemem->base = dt_mem_next_cell(dt_root_addr_cells, &reg);
>>>>> -	usablemem->size = dt_mem_next_cell(dt_root_size_cells, &reg);
>>>>> +	endp = reg + (len / sizeof(__be32));
>>>>> +	while ((endp - reg) >= (dt_root_addr_cells + dt_root_size_cells)) {
>>>>> +		usablemem[nr].base = dt_mem_next_cell(dt_root_addr_cells, &reg);
>>>>> +		usablemem[nr].size = dt_mem_next_cell(dt_root_size_cells, &reg);
>>>>> +
>>>>> +		if (++nr >= CRASH_MAX_USABLE_RANGES)
>>>>> +			break;
>>>>> +	}
>>>>>  
>>>>>  	return 1;
>>>>>  }
>>>>>  
>>>>>  static void __init fdt_enforce_memory_region(void)
>>>>>  {
>>>>> -	struct memblock_region reg = {
>>>>> -		.size = 0,
>>>>> -	};
>>>>> -
>>>>> -	of_scan_flat_dt(early_init_dt_scan_usablemem, &reg);
>>>>> -
>>>>> -	if (reg.size)
>>>>> -		memblock_cap_memory_range(reg.base, reg.size);
>>>>> +	int i, cnt = 0;
>>>>> +	struct memblock_region regs[CRASH_MAX_USABLE_RANGES];
>>>>> +
>>>>> +	memset(regs, 0, sizeof(regs));
>>>>> +	of_scan_flat_dt(early_init_dt_scan_usablemem, regs);
>>>>> +
>>>>> +	for (i = 0; i < CRASH_MAX_USABLE_RANGES; i++)
>>>>> +		if (regs[i].size)
>>>>> +			cnt++;
>>>>> +		else
>>>>> +			break;
>>>>> +	if (cnt)
>>>>> +		memblock_cap_memory_ranges(regs, cnt);
>>>>
>>>> Why not simply call memblock_cap_memory_range() for each region?
>>>
>>> Function memblock_cap_memory_range() removes all memory type ranges except specified range.
>>> So if we call memblock_cap_memory_range() for each region simply, there will be no usable-memory
>>> on kdump capture kernel.
>>
>> Thanks for the clarification.
>> I still think that memblock_cap_memory_ranges() is overly complex. 
>>
>> How about doing something like this:
>>
>> Cap the memory range for [min(regs[*].start, max(regs[*].end)] and then
>> removing the range in the middle?
> 
> Yes, that would be ok. But that would do one more memblock_cap_memory_range operation.
> That is, if there are n regions, we need to do (n + 1) operations, which doesn't seem to
> matter.
> 
> I agree with you, your idea is better.
> 
> Thanks,
> Chen Zhou

Sorry, just ignore my previous reply, I got that wrong.

I think it carefully, we can cap the memory range for [min(regs[*].start, max(regs[*].end)]
firstly. But how to remove the middle ranges, we still can't use memblock_cap_memory_range()
directly and the extra remove operation may be complex.

For more than one regions, i think add a new memblock_cap_memory_ranges() may be better.
Besides, memblock_cap_memory_ranges() is also applicable for one region.

How about replace memblock_cap_memory_range() with memblock_cap_memory_ranges()?

Thanks,
Chen Zhou

> 
>>  
>>> Thanks,
>>> Chen Zhou
>>>
>>>>
>>>>>  }
>>>>>  
>>>>>  void __init arm64_memblock_init(void)
>>>>> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
>>>>> index 47e3c06..aeade34 100644
>>>>> --- a/include/linux/memblock.h
>>>>> +++ b/include/linux/memblock.h
>>>>> @@ -446,6 +446,7 @@ phys_addr_t memblock_start_of_DRAM(void);
>>>>>  phys_addr_t memblock_end_of_DRAM(void);
>>>>>  void memblock_enforce_memory_limit(phys_addr_t memory_limit);
>>>>>  void memblock_cap_memory_range(phys_addr_t base, phys_addr_t size);
>>>>> +void memblock_cap_memory_ranges(struct memblock_region *regs, int cnt);
>>>>>  void memblock_mem_limit_remove_map(phys_addr_t limit);
>>>>>  bool memblock_is_memory(phys_addr_t addr);
>>>>>  bool memblock_is_map_memory(phys_addr_t addr);
>>>>> diff --git a/mm/memblock.c b/mm/memblock.c
>>>>> index 28fa8926..1a7f4ee7c 100644
>>>>> --- a/mm/memblock.c
>>>>> +++ b/mm/memblock.c
>>>>> @@ -1697,6 +1697,46 @@ void __init memblock_cap_memory_range(phys_addr_t base, phys_addr_t size)
>>>>>  			base + size, PHYS_ADDR_MAX);
>>>>>  }
>>>>>  
>>>>> +void __init memblock_cap_memory_ranges(struct memblock_region *regs, int cnt)
>>>>> +{
>>>>> +	int start_rgn[INIT_MEMBLOCK_REGIONS], end_rgn[INIT_MEMBLOCK_REGIONS];
>>>>> +	int i, j, ret, nr = 0;
>>>>> +
>>>>> +	for (i = 0; i < cnt; i++) {
>>>>> +		ret = memblock_isolate_range(&memblock.memory, regs[i].base,
>>>>> +				regs[i].size, &start_rgn[i], &end_rgn[i]);
>>>>> +		if (ret)
>>>>> +			break;
>>>>> +		nr++;
>>>>> +	}
>>>>> +	if (!nr)
>>>>> +		return;
>>>>> +
>>>>> +	/* remove all the MAP regions */
>>>>> +	for (i = memblock.memory.cnt - 1; i >= end_rgn[nr - 1]; i--)
>>>>> +		if (!memblock_is_nomap(&memblock.memory.regions[i]))
>>>>> +			memblock_remove_region(&memblock.memory, i);
>>>>> +
>>>>> +	for (i = nr - 1; i > 0; i--)
>>>>> +		for (j = start_rgn[i] - 1; j >= end_rgn[i - 1]; j--)
>>>>> +			if (!memblock_is_nomap(&memblock.memory.regions[j]))
>>>>> +				memblock_remove_region(&memblock.memory, j);
>>>>> +
>>>>> +	for (i = start_rgn[0] - 1; i >= 0; i--)
>>>>> +		if (!memblock_is_nomap(&memblock.memory.regions[i]))
>>>>> +			memblock_remove_region(&memblock.memory, i);
>>>>> +
>>>>> +	/* truncate the reserved regions */
>>>>> +	memblock_remove_range(&memblock.reserved, 0, regs[0].base);
>>>>> +
>>>>> +	for (i = nr - 1; i > 0; i--)
>>>>> +		memblock_remove_range(&memblock.reserved,
>>>>> +				regs[i].base, regs[i - 1].base + regs[i - 1].size);
>>>>> +
>>>>> +	memblock_remove_range(&memblock.reserved,
>>>>> +			regs[nr - 1].base + regs[nr - 1].size, PHYS_ADDR_MAX);
>>>>> +}
>>>>> +
>>>>>  void __init memblock_mem_limit_remove_map(phys_addr_t limit)
>>>>>  {
>>>>>  	phys_addr_t max_addr;
>>>>> -- 
>>>>> 2.7.4
>>>>>
>>>>
>>>
>>
> 
> 
> .
>