perf/x86/intel: Improve validation and configuration of ACR masks

In the Linux kernel, the following vulnerability has been resolved:

perf/x86/intel: Improve validation and configuration of ACR masks

Currently there are several issues on the user space ACR mask validation

and configuration.

- The validation for user space ACR mask (attr.config2) is incomplete,

e.g., the ACR mask could include the index which belongs to another

ACR events group, but it's not validated.

- An early return on an invalid ACR mask caused all subsequent ACR groups

to be skipped.

- The stale hardware ACR mask (hw.config1) is not cleared before setting

new hardware ACR mask.

The following changes address all of the above issues.

- Figure out the event index group of an ACR group. Any bits in the

user-space mask not present in the index group are now dropped.

- Instead of an early return on invalid bits, drop only the invalid

portions and continue iterating through all ACR events to ensure full

configuration.

- Explicitly clear the stale hardware ACR mask for each event prior to

writing the new configuration.

Besides, a non-leader event member of ACR group could be disabled in

theory. This could cause bit-shifting errors in the acr_mask of remaining

group members. But since ACR sampling requires all events to be active,

this should not be a big concern in real use case. Add a "FIXME" comment

to notice this risk.