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

Baoquan He
2022-08-02T03:08:15Z

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@redhat.com>

>
> Suggested-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.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
>
>
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