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SubjectRe: [patch v7 02/10] add prctl task isolation prctl docs and samples
On Fri, Nov 12, 2021 at 09:35:33AM -0300, Marcelo Tosatti wrote:
> +**PR_ISOL_CFG_GET**:
> +
> + Retrieve task isolation configuration.
> + The general format is::
> +
> + prctl(PR_ISOL_CFG_GET, what, arg3, arg4, arg5);
> +
> + The 'what' argument specifies what to configure. Possible values are:
> +
> + - ``I_CFG_FEAT``:
> +
> + Return configuration of task isolation features. The 'arg3' argument specifies
> + whether to return configured features (if zero), or individual
> + feature configuration (if not zero), as follows.
> +
> + - ``0``:
> +
> + Return the bitmask of configured features, in the location
> + pointed to by ``(int *)arg4``. The buffer should allow space
> + for 8 bytes.
> +
> + - ``ISOL_F_QUIESCE``:
> +
> + If arg4 is QUIESCE_CONTROL, return the control structure for
> + quiescing of background kernel activities, in the location
> + pointed to by ``(int *)arg5``::
> +
> + struct task_isol_quiesce_control {
> + __u64 flags;
> + __u64 quiesce_mask;
> + __u64 quiesce_oneshot_mask;
> + __u64 pad[5];
> + };
> +
> + See PR_ISOL_CFG_GET description for meaning of
> fields.

PR_ISOL_CFG_SET ?

[...]
> +
> + *quiesce_oneshot_mask*: A bitmask indicating which kernel
> + activities should behave in oneshot mode, that is, quiescing
> + will happen on return from prctl(PR_ISOL_ACTIVATE_SET), but not
> + on return of subsequent system calls. The corresponding bit(s)
> + must also be set at quiesce_mask.

Don't forget to mention interrupts and exceptions.

> +
> + *pad*: Additional space for future enhancements.
> +
> + For quiesce_mask (and quiesce_oneshot_mask), possible bit sets are:
> +
> + - ``ISOL_F_QUIESCE_VMSTATS``
> +
> + VM statistics are maintained in per-CPU counters to
> + improve performance. When a CPU modifies a VM statistic,
> + this modification is kept in the per-CPU counter.
> + Certain activities require a global count, which
> + involves requesting each CPU to flush its local counters
> + to the global VM counters.
> +
> + This flush is implemented via a workqueue item, which
> + might schedule a workqueue on isolated CPUs.
> +
> + To avoid this interruption, task isolation can be
> + configured to, upon return from system calls, synchronize
> + the per-CPU counters to global counters, thus avoiding
> + the interruption.
> +
> + - ``I_CFG_INHERIT``:
> + Set inheritance configuration when a new task
> + is created via fork and clone.
> +
> + The ``(int *)arg4`` argument is a pointer to::
> +
> + struct task_isol_inherit_control {
> + __u8 inherit_mask;
> + __u8 pad[7];
> + };
> +
> + inherit_mask is a bitmask that specifies which part
> + of task isolation should be inherited:
> +
> + - Bit ISOL_INHERIT_CONF: Inherit task isolation configuration.
> + This is the state written via prctl(PR_ISOL_CFG_SET, ...).
> +
> + - Bit ISOL_INHERIT_ACTIVE: Inherit task isolation activation
> + (requires ISOL_INHERIT_CONF to be set). The new task
> + should behave, after fork/clone, in the same manner
> + as the parent task after it executed:
> +
> + prctl(PR_ISOL_ACTIVATE_SET, &mask, ...);

I'm confused, what is the purpose of ISOL_INHERIT_CONF?

Thanks.

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