linux-kernel - Re: [PATCH RESEND] x86: don't reserve SETUP_RNG

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Message-ID: <Zd8AnmZHtR4ZGpoq@dwarf.suse.cz>
Date: Wed, 28 Feb 2024 10:45:02 +0100
From: Jiri Bohac <jbohac@...e.cz>
To: x86@...nel.org, "Jason A. Donenfeld" <Jason@...c4.com>,
	Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
	akpm@...ux-foundation.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] x86: don't reserve SETUP_RNG_SEED in e820

Adding Andrew Morton - have I been sending this to the wrong people/lists?

On Tue, Feb 20, 2024 at 02:55:27PM +0100, Jiri Bohac wrote:
> SETUP_RNG_SEED in setup_data is supplied by kexec and should
> not be reserved in the e820 map.
> 
> Doing so reserves 16 bytes of RAM when booting with kexec.
> (16 bytes because data->len is zeroed by parse_setup_data so only
> sizeof(setup_data) is reserved.)
> 
> When kexec is used repeatedly, each boot adds two entries in the
> kexec-provided e820 map as the 16-byte range splits a larger
> range of usable memory. Eventually all of the 128 available entries
> get used up. The next split will result in losing usable memory
> as the new entries cannot be added to the e820 map.
> 
> Fixes: 68b8e9713c8e ("x86/setup: Use rng seeds from setup_data")
> Signed-off-by: Jiri Bohac <jbohac@...e.cz>
> ---
>  arch/x86/kernel/e820.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index 91ade749f184..7be1362a31aa 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -1018,10 +1018,12 @@ void __init e820__reserve_setup_data(void)
>  		e820__range_update(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
>  
>  		/*
> -		 * SETUP_EFI and SETUP_IMA are supplied by kexec and do not need
> -		 * to be reserved.
> +		 * SETUP_EFI, SETUP_IMA and SETUP_RNG_SEED are supplied by
> +		 * kexec and do not need to be reserved.
>  		 */
> -		if (data->type != SETUP_EFI && data->type != SETUP_IMA)
> +		if (data->type != SETUP_EFI &&
> +		    data->type != SETUP_IMA &&
> +		    data->type != SETUP_RNG_SEED)
>  			e820__range_update_kexec(pa_data,
>  						 sizeof(*data) + data->len,
>  						 E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);

-- 
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, Prague, Czechia