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firmware_loader: Replace kmap() with kmap_local_page()

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The use of 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) kmap() 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.

kmap_local_page() is preferred over kmap() and kmap_atomic(). Where it
cannot mechanically replace the latters, code refactor should be considered
(special care must be taken if kernel virtual addresses are aliases in
different contexts).

With kmap_local_page() the mappings are per thread, CPU local, can take
page faults, and can be called from any context (including interrupts).

Call kmap_local_page() in firmware_loader wherever kmap() is currently
used. In firmware_rw() use the helpers copy_{from,to}_page() instead of
open coding the local mappings + memcpy().

Successfully tested with "firmware" selftests on a QEMU/KVM 32-bits VM
with 4GB RAM, booting a kernel with HIGHMEM64GB enabled.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Link: https://lore.kernel.org/r/20220714235030.12732-1-fmdefrancesco@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Fabio M. De Francesco
2022-07-15 01:50:30 +02:00
committed by Greg Kroah-Hartman
parent b18ee4a44e
commit f2d57765b7
2 changed files with 6 additions and 8 deletions
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4
drivers/base/firmware_loader/main.c
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@@ -435,11 +435,11 @@ static int fw_decompress_xz_pages(struct device *dev, struct fw_priv *fw_priv,
/* decompress onto the new allocated page */
page = fw_priv->pages[fw_priv->nr_pages - 1];
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);
fw_priv->size += xz_buf.out_pos;
/* partial decompression means either end or error */
if (xz_buf.out_pos != PAGE_SIZE)