2024-03-15 18:12:48

by Christian Göttsche

Subject: [PATCH v3] selinux: optimize ebitmap_and()

Iterate on nodes instead of single bits to save node resolution for each
single bit.

Similar to userspace patch efcd00814879 ("libsepol: optimize
ebitmap_and").

Signed-off-by: Christian Göttsche <[email protected]>
---
v3:
apply format style
v2:
fix array size computation
---
security/selinux/ss/ebitmap.c | 50 +++++++++++++++++++++++++++++------
1 file changed, 42 insertions(+), 8 deletions(-)

diff --git a/security/selinux/ss/ebitmap.c b/security/selinux/ss/ebitmap.c
index 67c1a73cd5ee..47cb90106118 100644
--- a/security/selinux/ss/ebitmap.c
+++ b/security/selinux/ss/ebitmap.c
@@ -78,19 +78,53 @@ int ebitmap_cpy(struct ebitmap *dst, const struct ebitmap *src)
int ebitmap_and(struct ebitmap *dst, const struct ebitmap *e1,
const struct ebitmap *e2)
{
- struct ebitmap_node *n;
- int bit, rc;
+ const struct ebitmap_node *n1, *n2;
+ struct ebitmap_node *new = NULL, **prev;

ebitmap_init(dst);

- ebitmap_for_each_positive_bit(e1, n, bit)
- {
- if (ebitmap_get_bit(e2, bit)) {
- rc = ebitmap_set_bit(dst, bit, 1);
- if (rc < 0)
- return rc;
+ prev = &dst->node;
+ n1 = e1->node;
+ n2 = e2->node;
+ while (n1 && n2) {
+ if (n1->startbit == n2->startbit) {
+ unsigned long testmap[EBITMAP_UNIT_NUMS];
+ unsigned int i;
+ bool match = false;
+
+ for (i = 0; i < ARRAY_SIZE(testmap); i++) {
+ testmap[i] = n1->maps[i] & n2->maps[i];
+ if (testmap[i] != 0)
+ match = true;
+ }
+
+ if (match) {
+ new = kmem_cache_zalloc(ebitmap_node_cachep,
+ GFP_ATOMIC);
+ if (!new) {
+ ebitmap_destroy(dst);
+ return -ENOMEM;
+ }
+ new->startbit = n1->startbit;
+ memcpy(new->maps, testmap, EBITMAP_SIZE / 8);
+ new->next = NULL;
+
+ *prev = new;
+ prev = &(new->next);
+ }
+
+ n1 = n1->next;
+ n2 = n2->next;
+ } else if (n1->startbit > n2->startbit) {
+ n2 = n2->next;
+ } else {
+ n1 = n1->next;
}
}
+
+ if (new)
+ dst->highbit = new->startbit + EBITMAP_SIZE;
+
return 0;
}

--
2.43.0

2024-03-27 22:08:11

by Paul Moore

Subject: Re: [PATCH v3] selinux: optimize ebitmap_and()

On Mar 15, 2024 =?UTF-8?q?Christian=20G=C3=B6ttsche?= <[email protected]> wrote:
>
> Iterate on nodes instead of single bits to save node resolution for each
> single bit.
>
> Similar to userspace patch efcd00814879 ("libsepol: optimize
> ebitmap_and").
>
> Signed-off-by: Christian Göttsche <[email protected]>
> ---
> v3:
> apply format style
> v2:
> fix array size computation
> ---
> security/selinux/ss/ebitmap.c | 50 +++++++++++++++++++++++++++++------
> 1 file changed, 42 insertions(+), 8 deletions(-)

Some minor comments below, but do you have any performance measurements
for this change? I realize that ebitmap_and() isn't widely used, but
it would be nice to understand the performance difference, and if there
isn't much/any difference we might want to stick with the original code
as it is much simpler.

> diff --git a/security/selinux/ss/ebitmap.c b/security/selinux/ss/ebitmap.c
> index 67c1a73cd5ee..47cb90106118 100644
> --- a/security/selinux/ss/ebitmap.c
> +++ b/security/selinux/ss/ebitmap.c
> @@ -78,19 +78,53 @@ int ebitmap_cpy(struct ebitmap *dst, const struct ebitmap *src)
> int ebitmap_and(struct ebitmap *dst, const struct ebitmap *e1,
> const struct ebitmap *e2)
> {
> - struct ebitmap_node *n;
> - int bit, rc;
> + const struct ebitmap_node *n1, *n2;
> + struct ebitmap_node *new = NULL, **prev;
>
> ebitmap_init(dst);
>
> - ebitmap_for_each_positive_bit(e1, n, bit)
> - {
> - if (ebitmap_get_bit(e2, bit)) {
> - rc = ebitmap_set_bit(dst, bit, 1);
> - if (rc < 0)
> - return rc;
> + prev = &dst->node;

Later in this function you include parenthesis, that might be nice
here too:

prev = &(dst->node);

> + n1 = e1->node;
> + n2 = e2->node;
> + while (n1 && n2) {
> + if (n1->startbit == n2->startbit) {
> + unsigned long testmap[EBITMAP_UNIT_NUMS];

This is very bikeshed-y, but I much prefer "dstmaps" over "testmap".

> + unsigned int i;
> + bool match = false;
> +
> + for (i = 0; i < ARRAY_SIZE(testmap); i++) {
> + testmap[i] = n1->maps[i] & n2->maps[i];
> + if (testmap[i] != 0)

If I'm going to be nitpicky, I'd probably prefer 'if (!dstmaps[i])'.

> + match = true;
> + }
> +
> + if (match) {
> + new = kmem_cache_zalloc(ebitmap_node_cachep,
> + GFP_ATOMIC);
> + if (!new) {
> + ebitmap_destroy(dst);
> + return -ENOMEM;
> + }
> + new->startbit = n1->startbit;
> + memcpy(new->maps, testmap, EBITMAP_SIZE / 8);

Why not just use 'sizeof(dstmaps)'?

memcpy(new->maps, dstmaps, sizeof(dstmaps));

> + new->next = NULL;

You shouldn't need the line above since you're doing a _zalloc().

> + *prev = new;
> + prev = &(new->next);
> + }
> +
> + n1 = n1->next;
> + n2 = n2->next;
> + } else if (n1->startbit > n2->startbit) {
> + n2 = n2->next;
> + } else {
> + n1 = n1->next;
> }
> }
> +
> + if (new)
> + dst->highbit = new->startbit + EBITMAP_SIZE;
> +
> return 0;
> }
>
> --
> 2.43.0

--
paul-moore.com