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

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Message-ID: <20250915114707.GB1024672@nvidia.com>
Date: Mon, 15 Sep 2025 08:47:07 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: 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,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	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 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:

	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);
 	}

Jason