linux-kernel - Re: [PATCHv7 1/7] kho: allow to drive kho from within kernel

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Message-ID: <aPnVrZC4Fz273lLn@kernel.org>
Date: Thu, 23 Oct 2025 10:13:49 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: akpm@...ux-foundation.org, brauner@...nel.org, corbet@....net,
	graf@...zon.com, jgg@...pe.ca, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
	masahiroy@...nel.org, ojeda@...nel.org, pratyush@...nel.org,
	rdunlap@...radead.org, tj@...nel.org
Subject: Re: [PATCHv7 1/7] kho: allow to drive kho from within kernel

On Tue, Oct 21, 2025 at 08:57:13PM -0400, Pasha Tatashin wrote:
> Allow kernel to drive finalize and abort without requiring triggers
> from the userspace.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> Reviewed-by: Pratyush Yadav <pratyush@...nel.org>

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

> ---
>  include/linux/kexec_handover.h | 15 +++++++
>  kernel/kexec_handover.c        | 75 +++++++++++++++++++++-------------
>  2 files changed, 61 insertions(+), 29 deletions(-)
> 
> diff --git a/include/linux/kexec_handover.h b/include/linux/kexec_handover.h
> index 25042c1d8d54..04d0108db98e 100644
> --- a/include/linux/kexec_handover.h
> +++ b/include/linux/kexec_handover.h
> @@ -67,6 +67,10 @@ void kho_memory_init(void);
>  
>  void kho_populate(phys_addr_t fdt_phys, u64 fdt_len, phys_addr_t scratch_phys,
>  		  u64 scratch_len);
> +
> +int kho_finalize(void);
> +int kho_abort(void);
> +
>  #else
>  static inline bool kho_is_enabled(void)
>  {
> @@ -139,6 +143,17 @@ static inline void kho_populate(phys_addr_t fdt_phys, u64 fdt_len,
>  				phys_addr_t scratch_phys, u64 scratch_len)
>  {
>  }
> +
> +static inline int kho_finalize(void)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline int kho_abort(void)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  #endif /* CONFIG_KEXEC_HANDOVER */
>  
>  #endif /* LINUX_KEXEC_HANDOVER_H */
> diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
> index de4466b47455..6458f369a346 100644
> --- a/kernel/kexec_handover.c
> +++ b/kernel/kexec_handover.c
> @@ -1087,7 +1087,7 @@ static int kho_out_update_debugfs_fdt(void)
>  	return err;
>  }
>  
> -static int kho_abort(void)
> +static int __kho_abort(void)
>  {
>  	int err;
>  	unsigned long order;
> @@ -1120,7 +1120,27 @@ static int kho_abort(void)
>  	return err;
>  }
>  
> -static int kho_finalize(void)
> +int kho_abort(void)
> +{
> +	int ret = 0;
> +
> +	if (!kho_enable)
> +		return -EOPNOTSUPP;
> +
> +	guard(mutex)(&kho_out.lock);
> +	if (!kho_out.finalized)
> +		return -ENOENT;
> +
> +	ret = __kho_abort();
> +	if (ret)
> +		return ret;
> +
> +	kho_out.finalized = false;
> +
> +	return kho_out_update_debugfs_fdt();
> +}
> +
> +static int __kho_finalize(void)
>  {
>  	int err = 0;
>  	u64 *preserved_mem_map;
> @@ -1163,12 +1183,32 @@ static int kho_finalize(void)
>  abort:
>  	if (err) {
>  		pr_err("Failed to convert KHO state tree: %d\n", err);
> -		kho_abort();
> +		__kho_abort();
>  	}
>  
>  	return err;
>  }
>  
> +int kho_finalize(void)
> +{
> +	int ret;
> +
> +	if (!kho_enable)
> +		return -EOPNOTSUPP;
> +
> +	guard(mutex)(&kho_out.lock);
> +	if (kho_out.finalized)
> +		return -EEXIST;
> +
> +	ret = __kho_finalize();
> +	if (ret)
> +		return ret;
> +
> +	kho_out.finalized = true;
> +
> +	return kho_out_update_debugfs_fdt();
> +}
> +
>  static int kho_out_finalize_get(void *data, u64 *val)
>  {
>  	mutex_lock(&kho_out.lock);
> @@ -1178,35 +1218,12 @@ static int kho_out_finalize_get(void *data, u64 *val)
>  	return 0;
>  }
>  
> -static int kho_out_finalize_set(void *data, u64 _val)
> +static int kho_out_finalize_set(void *data, u64 val)
>  {
> -	int ret = 0;
> -	bool val = !!_val;
> -
> -	mutex_lock(&kho_out.lock);
> -
> -	if (val == kho_out.finalized) {
> -		if (kho_out.finalized)
> -			ret = -EEXIST;
> -		else
> -			ret = -ENOENT;
> -		goto unlock;
> -	}
> -
>  	if (val)
> -		ret = kho_finalize();
> +		return kho_finalize();
>  	else
> -		ret = kho_abort();
> -
> -	if (ret)
> -		goto unlock;
> -
> -	kho_out.finalized = val;
> -	ret = kho_out_update_debugfs_fdt();
> -
> -unlock:
> -	mutex_unlock(&kho_out.lock);
> -	return ret;
> +		return kho_abort();
>  }
>  
>  DEFINE_DEBUGFS_ATTRIBUTE(fops_kho_out_finalize, kho_out_finalize_get,
> -- 
> 2.51.0.915.g61a8936c21-goog
> 

-- 
Sincerely yours,
Mike.