The use of kmap() is being deprecated in favor of kmap_local_page().
There are two main problems with kmap(): (1) It comes with an overhead as
the 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).
It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
the tasks can be preempted and, when they are scheduled to run again, the
kernel virtual addresses are restored and still valid.
Since its use in fs/ecryptfs is safe everywhere, it should be preferred.
Therefore, replace kmap() with kmap_local_page() in fs/ecryptfs.
Cc: "Venkataramanan, Anirudh" <[email protected]>
Suggested-by: Ira Weiny <[email protected]>
Reviewed-by: Ira Weiny <[email protected]>
Signed-off-by: Fabio M. De Francesco <[email protected]>
---
I'm resending this patch because some recipients were missing in the
previous submission. In the meantime I'm also adding some more information
in the commit message. There are no changes in the code.
fs/ecryptfs/crypto.c | 8 ++++----
fs/ecryptfs/read_write.c | 8 ++++----
2 files changed, 8 insertions(+), 8 deletions(-)
diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index e3f5d7f3c8a0..03263ebcccc6 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -465,10 +465,10 @@ int ecryptfs_encrypt_page(struct page *page)
}
lower_offset = lower_offset_for_page(crypt_stat, page);
- enc_extent_virt = kmap(enc_extent_page);
+ enc_extent_virt = kmap_local_page(enc_extent_page);
rc = ecryptfs_write_lower(ecryptfs_inode, enc_extent_virt, lower_offset,
PAGE_SIZE);
- kunmap(enc_extent_page);
+ kunmap_local(enc_extent_virt);
if (rc < 0) {
ecryptfs_printk(KERN_ERR,
"Error attempting to write lower page; rc = [%d]\n",
@@ -514,10 +514,10 @@ int ecryptfs_decrypt_page(struct page *page)
BUG_ON(!(crypt_stat->flags & ECRYPTFS_ENCRYPTED));
lower_offset = lower_offset_for_page(crypt_stat, page);
- page_virt = kmap(page);
+ page_virt = kmap_local_page(page);
rc = ecryptfs_read_lower(page_virt, lower_offset, PAGE_SIZE,
ecryptfs_inode);
- kunmap(page);
+ kunmap_local(page_virt);
if (rc < 0) {
ecryptfs_printk(KERN_ERR,
"Error attempting to read lower page; rc = [%d]\n",
diff --git a/fs/ecryptfs/read_write.c b/fs/ecryptfs/read_write.c
index 60bdcaddcbe5..5edf027c8359 100644
--- a/fs/ecryptfs/read_write.c
+++ b/fs/ecryptfs/read_write.c
@@ -64,11 +64,11 @@ int ecryptfs_write_lower_page_segment(struct inode *ecryptfs_inode,
offset = ((((loff_t)page_for_lower->index) << PAGE_SHIFT)
+ offset_in_page);
- virt = kmap(page_for_lower);
+ virt = kmap_local_page(page_for_lower);
rc = ecryptfs_write_lower(ecryptfs_inode, virt, offset, size);
if (rc > 0)
rc = 0;
- kunmap(page_for_lower);
+ kunmap_local(virt);
return rc;
}
@@ -253,11 +253,11 @@ int ecryptfs_read_lower_page_segment(struct page *page_for_ecryptfs,
int rc;
offset = ((((loff_t)page_index) << PAGE_SHIFT) + offset_in_page);
- virt = kmap(page_for_ecryptfs);
+ virt = kmap_local_page(page_for_ecryptfs);
rc = ecryptfs_read_lower(virt, offset, size, ecryptfs_inode);
if (rc > 0)
rc = 0;
- kunmap(page_for_ecryptfs);
+ kunmap_local(virt);
flush_dcache_page(page_for_ecryptfs);
return rc;
}
--
2.37.2
On 2022-09-01 18:07:04, Fabio M. De Francesco wrote:
> The use of kmap() is being deprecated in favor of kmap_local_page().
>
> There are two main problems with kmap(): (1) It comes with an overhead as
> the 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).
> It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
> the tasks can be preempted and, when they are scheduled to run again, the
> kernel virtual addresses are restored and still valid.
>
> Since its use in fs/ecryptfs is safe everywhere, it should be preferred.
>
> Therefore, replace kmap() with kmap_local_page() in fs/ecryptfs.
>
> Cc: "Venkataramanan, Anirudh" <[email protected]>
> Suggested-by: Ira Weiny <[email protected]>
> Reviewed-by: Ira Weiny <[email protected]>
> Signed-off-by: Fabio M. De Francesco <[email protected]>
> ---
>
> I'm resending this patch because some recipients were missing in the
> previous submission. In the meantime I'm also adding some more information
> in the commit message. There are no changes in the code.
Thanks for the additional information, Fabio. I've tested and applied
it.
Tyler
>
> fs/ecryptfs/crypto.c | 8 ++++----
> fs/ecryptfs/read_write.c | 8 ++++----
> 2 files changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
> index e3f5d7f3c8a0..03263ebcccc6 100644
> --- a/fs/ecryptfs/crypto.c
> +++ b/fs/ecryptfs/crypto.c
> @@ -465,10 +465,10 @@ int ecryptfs_encrypt_page(struct page *page)
> }
>
> lower_offset = lower_offset_for_page(crypt_stat, page);
> - enc_extent_virt = kmap(enc_extent_page);
> + enc_extent_virt = kmap_local_page(enc_extent_page);
> rc = ecryptfs_write_lower(ecryptfs_inode, enc_extent_virt, lower_offset,
> PAGE_SIZE);
> - kunmap(enc_extent_page);
> + kunmap_local(enc_extent_virt);
> if (rc < 0) {
> ecryptfs_printk(KERN_ERR,
> "Error attempting to write lower page; rc = [%d]\n",
> @@ -514,10 +514,10 @@ int ecryptfs_decrypt_page(struct page *page)
> BUG_ON(!(crypt_stat->flags & ECRYPTFS_ENCRYPTED));
>
> lower_offset = lower_offset_for_page(crypt_stat, page);
> - page_virt = kmap(page);
> + page_virt = kmap_local_page(page);
> rc = ecryptfs_read_lower(page_virt, lower_offset, PAGE_SIZE,
> ecryptfs_inode);
> - kunmap(page);
> + kunmap_local(page_virt);
> if (rc < 0) {
> ecryptfs_printk(KERN_ERR,
> "Error attempting to read lower page; rc = [%d]\n",
> diff --git a/fs/ecryptfs/read_write.c b/fs/ecryptfs/read_write.c
> index 60bdcaddcbe5..5edf027c8359 100644
> --- a/fs/ecryptfs/read_write.c
> +++ b/fs/ecryptfs/read_write.c
> @@ -64,11 +64,11 @@ int ecryptfs_write_lower_page_segment(struct inode *ecryptfs_inode,
>
> offset = ((((loff_t)page_for_lower->index) << PAGE_SHIFT)
> + offset_in_page);
> - virt = kmap(page_for_lower);
> + virt = kmap_local_page(page_for_lower);
> rc = ecryptfs_write_lower(ecryptfs_inode, virt, offset, size);
> if (rc > 0)
> rc = 0;
> - kunmap(page_for_lower);
> + kunmap_local(virt);
> return rc;
> }
>
> @@ -253,11 +253,11 @@ int ecryptfs_read_lower_page_segment(struct page *page_for_ecryptfs,
> int rc;
>
> offset = ((((loff_t)page_index) << PAGE_SHIFT) + offset_in_page);
> - virt = kmap(page_for_ecryptfs);
> + virt = kmap_local_page(page_for_ecryptfs);
> rc = ecryptfs_read_lower(virt, offset, size, ecryptfs_inode);
> if (rc > 0)
> rc = 0;
> - kunmap(page_for_ecryptfs);
> + kunmap_local(virt);
> flush_dcache_page(page_for_ecryptfs);
> return rc;
> }
> --
> 2.37.2
>