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

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Message-Id: <20220707231550.1484-1-fmdefrancesco@gmail.com>
Date:   Fri,  8 Jul 2022 01:15:50 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Eric Biederman <ebiederm@...ssion.com>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Ira Weiny <ira.weiny@...el.com>
Subject: [PATCH v2] 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 <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