linux-kernel - Re: [PATCH v2 1/1] of: fdt: Scan /memreserve/ last

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Date:   Mon, 10 Apr 2023 19:40:54 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Lucas Tanure <tanure@...ux.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, jbrunet@...libre.com,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        martin.blumenstingl@...glemail.com, narmstrong@...libre.com,
        stefan@...er.ch
Subject: Re: [PATCH v2 1/1] of: fdt: Scan /memreserve/ last

On Mon, Apr 10, 2023 at 08:00:17AM -0400, Lucas Tanure wrote:
> Change the order of scanning /memreserve/ and /reserved-memory node.
> /reserved-memory node should go first, as it has a more updated
> description of the memory regions and it can apply flags, like nomap.
> Also, /memreserve/ should avoid reserving regions described in
> /reserved-memory node.
> 
> Signed-off-by: Lucas Tanure <tanure@...ux.com>
> ---
>  drivers/of/fdt.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index d1a68b6d03b3..26e608d8025d 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -635,16 +635,21 @@ void __init early_init_fdt_scan_reserved_mem(void)
>  	if (!initial_boot_params)
>  		return;
>  
> +	fdt_scan_reserved_mem();
> +	fdt_reserve_elfcorehdr();
> +
>  	/* Process header /memreserve/ fields */
>  	for (n = 0; ; n++) {
>  		fdt_get_mem_rsv(initial_boot_params, n, &base, &size);
>  		if (!size)
>  			break;
> +		if (memblock_overlaps_region(&memblock.memory, base, size) &&
> +		    memblock_is_region_reserved(base, size))
> +			break;

I don't think this is really needed, it's ok to reserve the same ranges
multiple times.
Both checks are not cheap, so it'll be better to just reserve everything
both from performance and simplicity points of view.

> +
>  		memblock_reserve(base, size);
>  	}
>  
> -	fdt_scan_reserved_mem();
> -	fdt_reserve_elfcorehdr();
>  	fdt_init_reserved_mem();
>  }
>  
> -- 
> 2.40.0
> 

-- 
Sincerely yours,
Mike.