linux-kernel - Re: [PATCH v3 6/7] mm/memblock: Use KSTATE instead of kho to preserve preserved_mem

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <893401bc-4754-4c67-a82a-0c49c8e7f447@gmail.com>
Date: Thu, 18 Sep 2025 21:00:31 +0200
From: Andrey Ryabinin <ryabinin.a.a@...il.com>
To: Jason Gunthorpe <jgg@...dia.com>, Andrey Ryabinin <arbn@...dex-team.com>
Cc: linux-kernel@...r.kernel.org, Alexander Graf <graf@...zon.com>,
 Mike Rapoport <rppt@...nel.org>, James Gowans <jgowans@...zon.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Baoquan He
 <bhe@...hat.com>, kexec@...ts.infradead.org,
 Pratyush Yadav <ptyadav@...zon.de>,
 Pasha Tatashin <pasha.tatashin@...een.com>,
 David Rientjes <rientjes@...gle.com>, Pratyush Yadav <pratyush@...nel.org>,
 Changyuan Lyu <changyuanl@...gle.com>, Jonathan Corbet <corbet@....net>,
 linux-doc@...r.kernel.org, Chris Li <chrisl@...nel.org>,
 Ashish.Kalra@....com, William Tu <witu@...dia.com>,
 David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v3 6/7] mm/memblock: Use KSTATE instead of kho to preserve
 preserved_mem_table

On 9/15/25 1:47 PM, Jason Gunthorpe wrote:
> On Tue, Sep 09, 2025 at 10:14:41PM +0200, Andrey Ryabinin wrote:
>> +static int kstate_preserve_phys(struct kstate_stream *stream, void *obj,
>> +				const struct kstate_field *field)
>> +{
>> +	struct reserve_mem_table *map = obj;
>> +
>> +	return kho_preserve_phys(map->start, map->size);
>> +}
>> +
>> +struct kstate_description kstate_reserve_mem = {
>> +	.name = "reserved_mem",
>> +	.id = KSTATE_RESERVED_MEM_ID,
>> +	.fields = (const struct kstate_field[]) {
>> +		KSTATE_BASE_TYPE(name, struct reserve_mem_table,
>> +				char[RESERVE_MEM_NAME_SIZE]),
>> +		KSTATE_BASE_TYPE(start, struct reserve_mem_table, phys_addr_t),
>> +		KSTATE_BASE_TYPE(size, struct reserve_mem_table, phys_addr_t),
>> +		{
>> +			.name = "phys_range",
>> +			.flags = KS_CUSTOM,
>> +			.save = kstate_preserve_phys,
>> +		},
>> +		KSTATE_END_OF_LIST(),
>> +	},
>> +};
>>  
>>  static int __init reserve_mem_init(void)
>>  {
>>  	int err;
>> +	int i;
>>  
>>  	if (!kho_is_enabled() || !reserved_mem_count)
>>  		return 0;
>>  
>> +	for (i = 0; i < reserved_mem_count; i++) {
>> +		struct reserve_mem_table *map = &reserved_mem_table[i];
>>  
>> +		err = kstate_register(&kstate_reserve_mem,
>> +				map, crc32(~0, map->name, RESERVE_MEM_NAME_SIZE));
>> +		if (err)
>> +			goto out;
>>  	}
> 
> As I've said to the other proposals, this doesn't seem to be bringing
> that much value compared to just using a normal struct:

We expect to have many such ABI maps across the kernel.
These maps will share common elements - simple types, folios, and preserved
regions.

With the approach you're suggesting, we'd need to re-implement the same
preserve/unpreserve/recover logic, error handling, and unwind code for
every individual ABI map. That quickly becomes repetitive and error-prone.

By contrast, KSTATE centralizes this logic. It avoids duplicating code
and lets us express the preservation details declaratively instead
of re-implementing them per struct.

> 	for (i = 0; i < reserved_mem_count; i++) {
> 		struct reserve_mem_table *map = &reserved_mem_table[i];
> 		struct khoser_reserve_mem_table abi_map = {.name = map->name. .start = map->start, .size = map->size};
> 
> 		err = kho_preserve_phys(map->start, map->size);
> 		if (err)
> 		    return err; // Should unwind the other preservations!
> 		
> 		luo_preserve_key(luo_obj, map->name, &abi_map, sizeof(abi_map), VERSION_0);

On the versioning side:
With this approach, introducing a new ABI version (say, abi_map_v1)
would require us to maintain restore logic for each supported version,
and carefully handle upgrades between them.

With KSTATE, versioning is built in. For example, adding a new field can
simply be expressed as:
 	KSTATE_BASE_TYPE_V(new_field, struct reserve_mem_table, int, 1);
This way, the framework handles compatibility, and we don’t need to manually
write version-specific restore paths for each ABI map.