linux-kernel - Re: [PATCH 2/2] kho: warn and exit when unpreserved page wasn't preserved

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Message-ID: <aQoOinskO4_BzzeQ@kernel.org>
Date: Tue, 4 Nov 2025 16:32:42 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Pratyush Yadav <pratyush@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>,
	Alexander Graf <graf@...zon.com>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	kexec@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kho: warn and exit when unpreserved page wasn't
 preserved

On Mon, Nov 03, 2025 at 07:02:32PM +0100, Pratyush Yadav wrote:
> Calling __kho_unpreserve() on a pair of (pfn, end_pfn) that wasn't
> preserved is a bug. Currently, if that is done, the physxa or bits can
> be NULL. This results in a soft lockup since a NULL physxa or bits
> results in redoing the loop without ever making any progress.
> 
> Return when physxa or bits are not found, but WARN first to loudly
> indicate invalid behaviour.
> 
> Fixes: fc33e4b44b271 ("kexec: enable KHO support for memory preservation")
> Signed-off-by: Pratyush Yadav <pratyush@...nel.org>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>

> ---
>  kernel/kexec_handover.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index c2bcbb10918ce..e5fd833726226 100644
> --- a/kernel/kexec_handover.c
> +++ b/kernel/kexec_handover.c
> @@ -167,12 +167,12 @@ static void __kho_unpreserve(struct kho_mem_track *track, unsigned long pfn,
>  		const unsigned long pfn_high = pfn >> order;
>  
>  		physxa = xa_load(&track->orders, order);
> -		if (!physxa)
> -			continue;
> +		if (WARN_ON_ONCE(!physxa))
> +			return;
>  
>  		bits = xa_load(&physxa->phys_bits, pfn_high / PRESERVE_BITS);
> -		if (!bits)
> -			continue;
> +		if (WARN_ON_ONCE(!bits))
> +			return;
>  
>  		clear_bit(pfn_high % PRESERVE_BITS, bits->preserve);
>  
> -- 
> 2.47.3
> 

-- 
Sincerely yours,
Mike.