linux-kernel - Re: [PATCH v2] kexec: Replace kmap() with kmap_local_page()

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Date:   Tue, 2 Aug 2022 11:06:54 +0800
From:   Baoquan He <bhe@...hat.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Cc:     Eric Biederman <ebiederm@...ssion.com>, kexec@...ts.infradead.org,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH v2] kexec: Replace kmap() with kmap_local_page()

On 07/08/22 at 01:15am, Fabio M. De Francesco wrote:
> The use of kmap() and kmap_atomic() are being deprecated in favor of
> kmap_local_page().
> 
> With kmap_local_page(), the mappings are per thread, CPU local and not
> globally visible. Furthermore, the mappings can be acquired from any
> context (including interrupts).
> 
> Therefore, use kmap_local_page() in kexec_core.c because these mappings are
> per thread, CPU local, and not globally visible.
> 
> Tested on a QEMU + KVM 32-bits VM booting a kernel with HIGHMEM64GB
> enabled.

Wondering what arch you tested with. 

This looks good, but may not benefit much. Say so because I doubt
how many 32bit systems are using kexec/kdump mechanism.

Anyway, 

Acked-by: Baoquan He <bhe@...hat.com>

> 
> Suggested-by: Ira Weiny <ira.weiny@...el.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
> ---
> 
> v1->v2: A sentence of the commit message contained an error due to a
> mistake in copy-pasting from a previous patch. Replace "aio.c" with
> "kexec_core.c".
> 
>  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 4d34c78334ce..6f98274765d4 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -814,7 +814,7 @@ static int kimage_load_normal_segment(struct kimage *image,
>  		if (result < 0)
>  			goto out;
>  
> -		ptr = kmap(page);
> +		ptr = kmap_local_page(page);
>  		/* Start with a clear page */
>  		clear_page(ptr);
>  		ptr += maddr & ~PAGE_MASK;
> @@ -827,7 +827,7 @@ static int kimage_load_normal_segment(struct kimage *image,
>  			memcpy(ptr, kbuf, uchunk);
>  		else
>  			result = copy_from_user(ptr, buf, uchunk);
> -		kunmap(page);
> +		kunmap_local(ptr);
>  		if (result) {
>  			result = -EFAULT;
>  			goto out;
> @@ -878,7 +878,7 @@ static int kimage_load_crash_segment(struct kimage *image,
>  			goto out;
>  		}
>  		arch_kexec_post_alloc_pages(page_address(page), 1, 0);
> -		ptr = kmap(page);
> +		ptr = kmap_local_page(page);
>  		ptr += maddr & ~PAGE_MASK;
>  		mchunk = min_t(size_t, mbytes,
>  				PAGE_SIZE - (maddr & ~PAGE_MASK));
> @@ -894,7 +894,7 @@ static int kimage_load_crash_segment(struct kimage *image,
>  		else
>  			result = copy_from_user(ptr, buf, uchunk);
>  		kexec_flush_icache_page(page);
> -		kunmap(page);
> +		kunmap_local(ptr);
>  		arch_kexec_pre_free_pages(page_address(page), 1);
>  		if (result) {
>  			result = -EFAULT;
> -- 
> 2.36.1
> 
> 
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
> 

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