Re: [PATCH v4] x86/PoD: tie together P2M update and increment of entry count

[George Dunlap <george.dunlap@xxxxxxxxx>]

On Wed, Mar 13, 2024 at 2:00 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> When not holding the PoD lock across the entire region covering P2M
> update and stats update, the entry count - if to be incorrect at all -
> should indicate too large a value in preference to a too small one, to
> avoid functions bailing early when they find the count is zero. However,
> instead of moving the increment ahead (and adjust back upon failure),
> extend the PoD-locked region.
>
> Fixes: 99af3cd40b6e ("x86/mm: Rework locking in the PoD layer")
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Would you mind commenting on why you went with multiple unlocks,
rather than multiple if statements?

e.g.,

```
rc = p2m_set_entry(...);

/* Do the pod entry adjustment while holding the lock on success */
if ( rc == 0 ) {
 /* adjust pod entries */
}

pod_unlock(p2m);

/* Do the rest of the clean-up and error handling */
if (rc == 0 ) {
```

Just right now the multiple unlocks makes me worry that we may forget
one at some point.

 -George