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 Signed-off-by: Fabio M. De Francesco fmdefrancesco@gmail.com ---
v1->v2: According to the comments from Greg Kroah-Hartman (thanks!), extend the commit message adding information about why kmap() should be avoided. Delete an unused variable left in the code of v1, which has been Reported-by: kernel test robot lkp@intel.com
drivers/base/firmware_loader/main.c | 4 ++-- drivers/base/firmware_loader/sysfs.c | 10 ++++------ 2 files changed, 6 insertions(+), 8 deletions(-)
diff --git a/drivers/base/firmware_loader/main.c b/drivers/base/firmware_loader/main.c index ac3f34e80194..7c3590fd97c2 100644 --- a/drivers/base/firmware_loader/main.c +++ b/drivers/base/firmware_loader/main.c @@ -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) diff --git a/drivers/base/firmware_loader/sysfs.c b/drivers/base/firmware_loader/sysfs.c index 5b0b85b70b6f..77bad32c481a 100644 --- a/drivers/base/firmware_loader/sysfs.c +++ b/drivers/base/firmware_loader/sysfs.c @@ -242,19 +242,17 @@ static void firmware_rw(struct fw_priv *fw_priv, char *buffer, loff_t offset, size_t count, bool read) { while (count) { - void *page_data; int page_nr = offset >> PAGE_SHIFT; int page_ofs = offset & (PAGE_SIZE - 1); int page_cnt = min_t(size_t, PAGE_SIZE - page_ofs, count);
- page_data = kmap(fw_priv->pages[page_nr]); - if (read) - memcpy(buffer, page_data + page_ofs, page_cnt); + memcpy_from_page(buffer, fw_priv->pages[page_nr], + page_ofs, page_cnt); else - memcpy(page_data + page_ofs, buffer, page_cnt); + memcpy_to_page(fw_priv->pages[page_nr], page_ofs, + buffer, page_cnt);
- kunmap(fw_priv->pages[page_nr]); buffer += page_cnt; offset += page_cnt; count -= page_cnt;