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Date: Fri, 26 Apr 2024 09:52:30 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
To: Byungchul Park <byungchul@sk.com>, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
        jbohac@suse.cz, dyoung@redhat.com
CC: kernel_team@skhynix.com, linux-kernel@vger.kernel.org
Subject: =?US-ASCII?Q?Re=3A_=5BPATCH_v2=5D_x86/e820=3A_apply_=27mem=3D=27_boot_co?=
 =?US-ASCII?Q?mmand_while_reserving_memory_using_boot=5Fparams?=
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On April 25, 2024 9:40:18 PM PDT, Byungchul Park <byungchul@sk=2Ecom> wrote=
:
>On Wed, Apr 24, 2024 at 10:03:13AM +0900, Byungchul Park wrote:
>> I might miss something=2E  Please lemme know if I go wrong=2E  Thanks=
=2E
>
>I started to work on it since I wanted to limit memory boundary using
>'mem=3D' boot command but it doesn't work=2E  However, while looking arou=
nd
>the code in more detail, I found the issue is about which one should
>have higher priority between:
>
>   1=2E boot command limiting memory boundary e=2Eg=2E 'mem=3D',
>   2=2E setup data of memory map from bootloader, boot_params=2E
>
>Based on the current code, setup data from bootloader has higher
>priority than boot command so the setup data can overwrite the user
>defined limit specified in boot command=2E  Is it inteded?
>
>   If yes, I should stop posting=2E
>   If not, I will keep posting with the following - v3=2E
>
>	Byungchul
>
>---
>
>diff --git a/arch/x86/kernel/e820=2Ec b/arch/x86/kernel/e820=2Ec
>index 6f1b379e3b38=2E=2E3bc593235b76 100644
>--- a/arch/x86/kernel/e820=2Ec
>+++ b/arch/x86/kernel/e820=2Ec
>@@ -879,6 +879,7 @@ static void __init early_panic(char *msg)
> }
>=20
> static int userdef __initdata;
>+static u64 userdef_mem_limit;
>=20
> /* The "mem=3Dnopentium" boot option disables 4MB page tables on 32-bit =
kernels: */
> static int __init parse_memopt(char *p)
>@@ -905,7 +906,10 @@ static int __init parse_memopt(char *p)
> 	if (mem_size =3D=3D 0)
> 		return -EINVAL;
>=20
>-	e820__range_remove(mem_size, ULLONG_MAX - mem_size, E820_TYPE_RAM, 1);
>+	if (userdef_mem_limit)
>+		userdef_mem_limit =3D min(userdef_mem_limit, mem_size);
>+	else
>+		userdef_mem_limit =3D mem_size;
>=20
> #ifdef CONFIG_MEMORY_HOTPLUG
> 	max_mem_size =3D mem_size;
>@@ -966,7 +970,10 @@ static int __init parse_memmap_one(char *p)
> 		else
> 			e820__range_remove(start_at, mem_size, 0, 0);
> 	} else {
>-		e820__range_remove(mem_size, ULLONG_MAX - mem_size, E820_TYPE_RAM, 1);
>+		if (userdef_mem_limit)
>+			userdef_mem_limit =3D min(userdef_mem_limit, mem_size);
>+		else
>+			userdef_mem_limit =3D mem_size;
> 	}
>=20
> 	return *p =3D=3D '\0' ? 0 : -EINVAL;
>@@ -1050,6 +1057,11 @@ void __init e820__reserve_setup_data(void)
> void __init e820__finish_early_params(void)
> {
> 	if (userdef) {
>+		if (userdef_mem_limit)
>+			e820__range_remove(userdef_mem_limit,
>+					ULLONG_MAX - userdef_mem_limit,
>+					E820_TYPE_RAM, 1);
>+
> 		if (e820__update_table(e820_table) < 0)
> 			early_panic("Invalid user supplied memory map");
>=20
>---
>> 	Byungchul
>>=20
>> Changes from v1
>> 	1=2E before - handle boot_mem_limit assuming the default is U64_MAX=2E
>> 	   after  - handle boot_mem_limit assuming the default is 0=2E
>>=20
>> --->8---
>> >From e8bf247d6024b35af5300914dcff9135df9c1d66 Mon Sep 17 00:00:00 2001
>> From: Byungchul Park <byungchul@sk=2Ecom>
>> Date: Wed, 24 Apr 2024 09:55:25 +0900
>> Subject: [PATCH v2] x86/e820: apply 'mem=3D' boot command while reservi=
ng memory using boot_params
>>=20
>> When a user specifies 'mem=3D' boot command, it's expected to limit the
>> maximum address of usable memory for the kernel no matter what the
>> memory map source is=2E  However, 'mem=3D' boot command doesn't work si=
nce
>> it doesn't respect it when reserving memory using boot_params=2E
>>=20
>> Applied the restriction when reserving memory using boot_params=2E  Whi=
le
>> at it, renamed mem_size to a more specific name, boot_mem_limit=2E
>>=20
>> Signed-off-by: Byungchul Park <byungchul@sk=2Ecom>
>> ---
>>  arch/x86/kernel/e820=2Ec | 15 +++++++++------
>>  1 file changed, 9 insertions(+), 6 deletions(-)
>>=20
>> diff --git a/arch/x86/kernel/e820=2Ec b/arch/x86/kernel/e820=2Ec
>> index 6f1b379e3b38=2E=2Ee3f716128caf 100644
>> --- a/arch/x86/kernel/e820=2Ec
>> +++ b/arch/x86/kernel/e820=2Ec
>> @@ -880,11 +880,11 @@ static void __init early_panic(char *msg)
>> =20
>>  static int userdef __initdata;
>> =20
>> +static u64 boot_mem_limit;
>> +
>>  /* The "mem=3Dnopentium" boot option disables 4MB page tables on 32-bi=
t kernels: */
>>  static int __init parse_memopt(char *p)
>>  {
>> -	u64 mem_size;
>> -
>>  	if (!p)
>>  		return -EINVAL;
>> =20
>> @@ -899,16 +899,16 @@ static int __init parse_memopt(char *p)
>>  	}
>> =20
>>  	userdef =3D 1;
>> -	mem_size =3D memparse(p, &p);
>> +	boot_mem_limit =3D memparse(p, &p);
>> =20
>>  	/* Don't remove all memory when getting "mem=3D{invalid}" parameter: =
*/
>> -	if (mem_size =3D=3D 0)
>> +	if (boot_mem_limit =3D=3D 0)
>>  		return -EINVAL;
>> =20
>> -	e820__range_remove(mem_size, ULLONG_MAX - mem_size, E820_TYPE_RAM, 1)=
;
>> +	e820__range_remove(boot_mem_limit, ULLONG_MAX - boot_mem_limit, E820_=
TYPE_RAM, 1);
>> =20
>>  #ifdef CONFIG_MEMORY_HOTPLUG
>> -	max_mem_size =3D mem_size;
>> +	max_mem_size =3D boot_mem_limit;
>>  #endif
>> =20
>>  	return 0;
>> @@ -1036,6 +1036,9 @@ void __init e820__reserve_setup_data(void)
>>  		early_memunmap(data, len);
>>  	}
>> =20
>> +	if (boot_mem_limit)
>> +		e820__range_remove(boot_mem_limit, ULLONG_MAX - boot_mem_limit,
>> +				E820_TYPE_RESERVED_KERN, 1);
>>  	e820__update_table(e820_table);
>> =20
>>  	pr_info("extended physical RAM map:\n");
>> --=20
>> 2=2E17=2E1

mem=3D typically should cap the usable memory at that address=2E At one po=
int in history we also allowed it to add memory at the top, but modern syst=
ems have too complex memory maps; the memmap=3D option can be used for that=
, however=2E