2022-07-07 23:53:39

by Fabio M. De Francesco

Subject: [PATCH] kexec: Replace kmap() with kmap_local_page()

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.

Suggested-by: Ira Weiny <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
---

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

2022-07-07 23:56:06

by Fabio M. De Francesco

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

On venerdì 8 luglio 2022 01:14:12 CEST 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.
>
> Suggested-by: Ira Weiny <[email protected]>
> Signed-off-by: Fabio M. De Francesco <[email protected]>
> ---
>
> 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(-)
>
Sorry, another error... Please discard this patch because the version
number is missing in the subject.

The second version, hopefully final and correct, is at
https://lore.kernel.org/lkml/[email protected]/

Thank you,

Fabio