linux-kernel - Re: [PATCH] x86/boot/e820: add new chareater "-" to free BIOS memory in memmap bootargs

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Date:   Tue, 17 Apr 2018 22:40:54 +0800
From:   zoucao-ipc <zoucaox@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>, zoucao@...ux.alibaba.com
CC:     mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/boot/e820: add new chareater "-" to free BIOS memory
 in memmap bootargs


On 2018/4/17 下午9:47, Thomas Gleixner wrote:
> On Tue, 10 Apr 2018, zoucao@...ux.alibaba.com wrote:
>> From: zoucao <zoucao@...alhost.localdomain>
> Interesting from ... Please use your real mail address for this.
miss this, i will do it.
>> Normally every BIOS reserved memory is used for some features, we can't
>> use them, but in some conditions,  users can ensure some BIOS memories
>> are not used and reserved memory is well to free, they have not a good
>> way to free these memories, here add a new chareater "-" in memmap to
>> free reserved memory.
> I'm not really convinced about this. How should anyone without detailed
> BIOS knowledge know that this is really reusable?
>
> The person who knows must have access to the BIOS developer, so why can't
> the BIOS be fixed instead?
>
> Thanks,
>
> 	tglx
>
>> Signed-off-by: zou cao <zoucao@...ux.alibaba.com>
>> ---
>>   7u/Documentation/kernel-parameters.txt | 6 ++++++
>>   7u/arch/x86/kernel/e820.c              | 3 +++
>>   2 files changed, 9 insertions(+)
>>
>> diff --git a/7u/Documentation/kernel-parameters.txt b/7u/Documentation/kernel-parameters.txt
>> index 9a1abb99a..dbea75e12 100644
>> --- a/7u/Documentation/kernel-parameters.txt
>> +++ b/7u/Documentation/kernel-parameters.txt
>> @@ -1677,6 +1677,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>   			         or
>>   			         memmap=0x10000$0x18690000
>>   
>> +	memmap=nn[KMG]-ss[KMG]
>> +			Free E820 reserved memory, as specified by the user.
>> +			Region of reserved memory to be free, from ss to ss+nn.
>> +			Example: free reserved memory from 0x18690000-0x186a0000
>> +					memmap=0x4101000-0x6aeff000
>> +
>>   	memory_corruption_check=0/1 [X86]
>>   			Some BIOSes seem to corrupt the first 64k of
>>   			memory when doing things like suspend/resume.
>> diff --git a/7u/arch/x86/kernel/e820.c b/7u/arch/x86/kernel/e820.c
>> index 174da5fc5..b8a042981 100644
>> --- a/7u/arch/x86/kernel/e820.c
>> +++ b/7u/arch/x86/kernel/e820.c
>> @@ -875,6 +875,9 @@ static int __init parse_memmap_one(char *p)
>>   	} else if (*p == '$') {
>>   		start_at = memparse(p+1, &p);
>>   		e820_add_region(start_at, mem_size, E820_RESERVED);
>> +	} else if (*p == '-') {
>> +		start_at = memparse(p+1, &p);
>> +		e820_remove_range(start_at, mem_size, E820_RESERVED, E820_RAM);
>>   	} else
>>   		e820_remove_range(mem_size, ULLONG_MAX - mem_size, E820_RAM, 1);
>>   
>> -- 
>> 2.14.1.40.g8e62ba1
>>
>>