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authorFabio M. De Francesco <fmdefrancesco@gmail.com>2022-07-20 18:19:32 +0200
committerLuis Chamberlain <mcgrof@kernel.org>2022-07-20 14:27:46 -0700
commit554694ba120b87e39cf732ed632e6a0c52fafb7c (patch)
treef6d22932a8db1f5eea46f44cf43f2560f7e0eb9d /kernel/module
parent6f1dae1d84b6d08541d8e12edd1c8677ab279dea (diff)
module: Replace kmap() with kmap_local_page()
kmap() is being deprecated in favor of kmap_local_page(). Two main problems with kmap(): (1) It comes with an overhead as mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap’s pool wraps and it might block when the mapping space is fully utilized until a slot becomes available. With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts). Tasks can be preempted and, when scheduled to run again, the kernel virtual addresses are restored and still valid. kmap_local_page() is faster than kmap() in kernels with HIGHMEM enabled. Since the use of kmap_local_page() in module_gzip_decompress() and in module_xz_decompress() is safe (i.e., it does not break the strict rules of use), it should be preferred over kmap(). Therefore, replace kmap() with kmap_local_page(). Tested on a QEMU/KVM x86_32 VM with 4GB RAM, booting kernels with HIGHMEM64GB enabled. Modules compressed with XZ or GZIP decompress properly. Cc: Matthew Wilcox <willy@infradead.com> Suggested-by: Ira Weiny <ira.weiny@intel.com> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Diffstat (limited to 'kernel/module')
-rw-r--r--kernel/module/decompress.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/kernel/module/decompress.c b/kernel/module/decompress.c
index 2fc7081dd7c1..4d0bcb3d9e44 100644
--- a/kernel/module/decompress.c
+++ b/kernel/module/decompress.c
@@ -119,10 +119,10 @@ static ssize_t module_gzip_decompress(struct load_info *info,
goto out_inflate_end;
}
- s.next_out = kmap(page);
+ s.next_out = kmap_local_page(page);
s.avail_out = PAGE_SIZE;
rc = zlib_inflate(&s, 0);
- kunmap(page);
+ kunmap_local(s.next_out);
new_size += PAGE_SIZE - s.avail_out;
} while (rc == Z_OK);
@@ -178,11 +178,11 @@ static ssize_t module_xz_decompress(struct load_info *info,
goto out;
}
- xz_buf.out = kmap(page);
+ xz_buf.out = kmap_local_page(page);
xz_buf.out_pos = 0;
xz_buf.out_size = PAGE_SIZE;
xz_ret = xz_dec_run(xz_dec, &xz_buf);
- kunmap(page);
+ kunmap_local(xz_buf.out);
new_size += xz_buf.out_pos;
} while (xz_buf.out_pos == PAGE_SIZE && xz_ret == XZ_OK);