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Date: Sun, 4 Feb 2024 15:38:26 +0800
From: Baoquan He <bhe@redhat.com>
To: "yang.zhang" <gaoshanliukou@163.com>
Cc: ebiederm@xmission.com, kexec@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	"yang.zhang" <yang.zhang@hexintek.com>
Subject: Re: [PATCH] kexec: should use uchunk for user buffer increasing
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On 01/30/24 at 06:18pm, yang.zhang wrote:
> From: "yang.zhang" <yang.zhang@hexintek.com>
> 
> Because of alignment requirement in kexec-tools, there is
> no problem for user buffer increasing when loading segments.
> But when coping, the step is uchunk, so we should use uchunk
> not mchunk.

In theory, ubytes is <= mbytes. So uchunk is always <= mchunk. If ubytes
is exhausted, while there's still remaining mbytes, then uchunk is 0,
there's still mchunk stepping forward. If I understand it correctly,
this is a good catch. Not sure if Eric has comment on this to confirm.

static int kimage_load_normal_segment(struct kimage *image,
                                         struct kexec_segment *segment)
{
.....

                ptr += maddr & ~PAGE_MASK;
                mchunk = min_t(size_t, mbytes,
                                PAGE_SIZE - (maddr & ~PAGE_MASK));
                uchunk = min(ubytes, mchunk);
.....}

> 
> Signed-off-by: yang.zhang <yang.zhang@hexintek.com>
> ---
>  kernel/kexec_core.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index d08fc7b5db97..2b8354313c85 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -813,9 +813,9 @@ static int kimage_load_normal_segment(struct kimage *image,
>  		ubytes -= uchunk;
>  		maddr  += mchunk;
>  		if (image->file_mode)
> -			kbuf += mchunk;
> +			kbuf += uchunk;
>  		else
> -			buf += mchunk;
> +			buf += uchunk;
>  		mbytes -= mchunk;
>  
>  		cond_resched();
> @@ -881,9 +881,9 @@ static int kimage_load_crash_segment(struct kimage *image,
>  		ubytes -= uchunk;
>  		maddr  += mchunk;
>  		if (image->file_mode)
> -			kbuf += mchunk;
> +			kbuf += uchunk;
>  		else
> -			buf += mchunk;
> +			buf += uchunk;
>  		mbytes -= mchunk;
>  
>  		cond_resched();
> -- 
> 2.34.1
> 
> 
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