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fsverity updates for 6.9

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Slightly improve data verification performance by eliminating an
 unnecessary lock.
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Merge tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fsverity/linux

Pull fsverity update from Eric Biggers:
 "Slightly improve data verification performance by eliminating an
  unnecessary lock"

* tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fsverity/linux:
  fsverity: remove hash page spin lock
This commit is contained in:
Linus Torvalds 2024-03-12 13:22:10 -07:00
commit d453cc5a27
3 changed files with 24 additions and 26 deletions
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1
fs/verity/fsverity_private.h
View File

@ -69,7 +69,6 @@ struct fsverity_info {
u8 file_digest[FS_VERITY_MAX_DIGEST_SIZE];
const struct inode *inode;
unsigned long *hash_block_verified;
spinlock_t hash_page_init_lock;
};
#define FS_VERITY_MAX_SIGNATURE_SIZE (FS_VERITY_MAX_DESCRIPTOR_SIZE - \

1
fs/verity/open.c
View File

@ -239,7 +239,6 @@ struct fsverity_info *fsverity_create_info(const struct inode *inode,
err = -ENOMEM;
goto fail;
}
spin_lock_init(&vi->hash_page_init_lock);
}
return vi;

48
fs/verity/verify.c
View File

@ -19,7 +19,6 @@ static struct workqueue_struct *fsverity_read_workqueue;
static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage,
unsigned long hblock_idx)
{
bool verified;
unsigned int blocks_per_page;
unsigned int i;
@ -43,12 +42,20 @@ static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage,
* re-instantiated from the backing storage are re-verified. To do
* this, we use PG_checked again, but now it doesn't really mean
* "checked". Instead, now it just serves as an indicator for whether
* the hash page is newly instantiated or not.
* the hash page is newly instantiated or not. If the page is new, as
* indicated by PG_checked=0, we clear the bitmap bits for the page's
* blocks since they are untrustworthy, then set PG_checked=1.
* Otherwise we return the bitmap bit for the requested block.
*
* The first thread that sees PG_checked=0 must clear the corresponding
* bitmap bits, then set PG_checked=1. This requires a spinlock. To
* avoid having to take this spinlock in the common case of
* PG_checked=1, we start with an opportunistic lockless read.
* Multiple threads may execute this code concurrently on the same page.
* This is safe because we use memory barriers to ensure that if a
* thread sees PG_checked=1, then it also sees the associated bitmap
* clearing to have occurred. Also, all writes and their corresponding
* reads are atomic, and all writes are safe to repeat in the event that
* multiple threads get into the PG_checked=0 section. (Clearing a
* bitmap bit again at worst causes a hash block to be verified
* redundantly. That event should be very rare, so it's not worth using
* a lock to avoid. Setting PG_checked again has no effect.)
*/
if (PageChecked(hpage)) {
/*
@ -58,24 +65,17 @@ static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage,
smp_rmb();
return test_bit(hblock_idx, vi->hash_block_verified);
}
spin_lock(&vi->hash_page_init_lock);
if (PageChecked(hpage)) {
verified = test_bit(hblock_idx, vi->hash_block_verified);
} else {
blocks_per_page = vi->tree_params.blocks_per_page;
hblock_idx = round_down(hblock_idx, blocks_per_page);
for (i = 0; i < blocks_per_page; i++)
clear_bit(hblock_idx + i, vi->hash_block_verified);
/*
* A write memory barrier is needed here to give RELEASE
* semantics to the below SetPageChecked() operation.
*/
smp_wmb();
SetPageChecked(hpage);
verified = false;
}
spin_unlock(&vi->hash_page_init_lock);
return verified;
blocks_per_page = vi->tree_params.blocks_per_page;
hblock_idx = round_down(hblock_idx, blocks_per_page);
for (i = 0; i < blocks_per_page; i++)
clear_bit(hblock_idx + i, vi->hash_block_verified);
/*
* A write memory barrier is needed here to give RELEASE semantics to
* the below SetPageChecked() operation.
*/
smp_wmb();
SetPageChecked(hpage);
return false;
}
/*