linux-kernel - Re: [PATCH] kexec_core: Remove superfluous page offset handling in segment loading

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Message-ID: <aMKZUY/zg31qN+68@MiWiFi-R3L-srv>
Date: Thu, 11 Sep 2025 17:41:37 +0800
From: Baoquan He <bhe@...hat.com>
To: Justinien Bouron <jbouron@...zon.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Petr Mladek <pmladek@...e.com>,
	Mario Limonciello <mario.limonciello@....com>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Alexander Graf <graf@...zon.com>,
	Steven Chen <chenste@...ux.microsoft.com>,
	Yan Zhao <yan.y.zhao@...el.com>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Gunnar Kudrjavets <gunnarku@...zon.com>
Subject: Re: [PATCH] kexec_core: Remove superfluous page offset handling in
 segment loading

On 09/10/25 at 09:31am, Justinien Bouron wrote:
> Kexec does not accept segments for which the destination address is not
> page aligned. Therefore there is no need for page offset handling when
> loading segments.

Do you mean we will adjust the memsz and buf_align to PAGE_SIZE aligned
in kexec_add_buffer()? That better be explained in log.

int kexec_add_buffer(struct kexec_buf *kbuf)
{
	......
	/* Ensure minimum alignment needed for segments. */
        kbuf->memsz = ALIGN(kbuf->memsz, PAGE_SIZE);
        kbuf->buf_align = max(kbuf->buf_align, PAGE_SIZE);
        kbuf->cma = NULL;
	......
}

> 
> Signed-off-by: Justinien Bouron <jbouron@...zon.com>
> Reviewed-by: Gunnar Kudrjavets <gunnarku@...zon.com>
> ---
>  kernel/kexec_core.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 31203f0bacaf..7d4c9eebea79 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -761,9 +761,7 @@ static int kimage_load_cma_segment(struct kimage *image, int idx)
>  	while (mbytes) {
>  		size_t uchunk, mchunk;
>  
> -		ptr += maddr & ~PAGE_MASK;
> -		mchunk = min_t(size_t, mbytes,
> -				PAGE_SIZE - (maddr & ~PAGE_MASK));
> +		mchunk = min_t(size_t, mbytes, PAGE_SIZE);

I am not so eager to remove it as keeping it makes a little sense on
defensive programming. Surely, I am not opposing it as it's truly not
necessary for now.

>  		uchunk = min(ubytes, mchunk);
>  
>  		if (uchunk) {
> @@ -815,6 +813,7 @@ static int kimage_load_normal_segment(struct kimage *image, int idx)
>  	mbytes = segment->memsz;
>  	maddr = segment->mem;
>  
> +
>  	if (image->segment_cma[idx])
>  		return kimage_load_cma_segment(image, idx);
>  
> @@ -840,9 +839,7 @@ static int kimage_load_normal_segment(struct kimage *image, int idx)
>  		ptr = kmap_local_page(page);
>  		/* Start with a clear page */
>  		clear_page(ptr);
> -		ptr += maddr & ~PAGE_MASK;
> -		mchunk = min_t(size_t, mbytes,
> -				PAGE_SIZE - (maddr & ~PAGE_MASK));
> +		mchunk = min_t(size_t, mbytes, PAGE_SIZE);
>  		uchunk = min(ubytes, mchunk);
>  
>  		if (uchunk) {
> @@ -905,9 +902,7 @@ static int kimage_load_crash_segment(struct kimage *image, int idx)
>  		}
>  		arch_kexec_post_alloc_pages(page_address(page), 1, 0);
>  		ptr = kmap_local_page(page);
> -		ptr += maddr & ~PAGE_MASK;
> -		mchunk = min_t(size_t, mbytes,
> -				PAGE_SIZE - (maddr & ~PAGE_MASK));
> +		mchunk = min_t(size_t, mbytes, PAGE_SIZE);
>  		uchunk = min(ubytes, mchunk);
>  		if (mchunk > uchunk) {
>  			/* Zero the trailing part of the page */
> -- 
> 2.43.0
> 
>