linux-kernel - Re: [PATCH 1/3] kho: allow scratch areas with zero size

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Message-ID: <mafs0349vwd1i.fsf@kernel.org>
Date: Wed, 13 Aug 2025 15:45:29 +0200
From: Pratyush Yadav <pratyush@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,  Alexander Graf
 <graf@...zon.com>,  Baoquan He <bhe@...hat.com>,  Changyuan Lyu
 <changyuanl@...gle.com>,  Pasha Tatashin <pasha.tatashin@...een.com>,
  Pratyush Yadav <pratyush@...nel.org>,  Shuah Khan <shuah@...nel.org>,
  Thomas Weischuh <linux@...ssschuh.net>,  kexec@...ts.infradead.org,
  linux-kernel@...r.kernel.org,  linux-kselftest@...r.kernel.org,
  linux-mm@...ck.org
Subject: Re: [PATCH 1/3] kho: allow scratch areas with zero size

On Mon, Aug 11 2025, Mike Rapoport wrote:

> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
>
> Parsing of kho_scratch parameter treats zero size as an invalid value,
> although it should be fine for user to request zero sized scratch area
> for some types if scratch memory, when for example there is no need to
> create scratch area in the low memory.

Can the system boot with 0 per-node memory? If not, then perhaps we
should only allow lowmem scratch to be zero?

>
> Treat zero as a valid value for a scratch area size but reject
> kho_scratch parameter that defines no scratch memory at all.
>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> ---
>  kernel/kexec_handover.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index e49743ae52c5..c6ac5a5e51cb 100644
> --- a/kernel/kexec_handover.c
> +++ b/kernel/kexec_handover.c
> @@ -385,6 +385,7 @@ static int __init kho_parse_scratch_size(char *p)
>  {
>  	size_t len;
>  	unsigned long sizes[3];
> +	size_t total_size = 0;
>  	int i;
>  
>  	if (!p)
> @@ -421,11 +422,15 @@ static int __init kho_parse_scratch_size(char *p)
>  		}
>  
>  		sizes[i] = memparse(p, &endp);
> -		if (!sizes[i] || endp == p)
> +		if (endp == p)
>  			return -EINVAL;
>  		p = endp;
> +		total_size += sizes[i];
>  	}
>  
> +	if (!total_size)
> +		return -EINVAL;
> +

Looks good. BTW, unrelated to this patch, but should we also check that
p == '\0' here to make sure the whole argument was consumed?


>  	scratch_size_lowmem = sizes[0];
>  	scratch_size_global = sizes[1];
>  	scratch_size_pernode = sizes[2];

-- 
Regards,
Pratyush Yadav