Messages in this thread | | | Date | Tue, 06 Feb 2024 15:49:11 -0300 | From | Marcelo Tosatti <> | Subject | [patch 00/12] cpu isolation: infra to block interference to select CPUs |
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There are a number of codepaths in the kernel that interrupt code execution in remote CPUs. A subset of such codepaths are triggered from userspace and can therefore return errors.
Introduce a cpumask named "block interference", writable from userspace.
This cpumask (and associated helpers) can be used by code that executes code on remote CPUs to optionally return an error.
Note: the word "interference" has been chosen since "interruption" is often confused with "device interrupt".
To protect readers VS writers of this cpumask, SRCU protection is used.
What is proposed is to incrementally modify code that can return errors in two ways:
1) Introduction of fail variants of the functions that generate code execution on remote CPUs. This way the modified code should look like:
idx = block_interf_srcu_read_lock(); ret = smp_call_function_single_fail(cpu, remote_fn, ...); (or stop_machine_fail) block_interf_srcu_read_unlock(idx);
This is grep friendly (so one can search for smp_call_function_* variants) and re-uses code.
2) Usage of block interference CPU mask helpers. For certain users of smp_call_func_*, stop_machine_* functions it is natural to check for block interference CPUs before calling the functions for remote code execution.
For example if its not desirable to perform error handling at smp_call_func_* time, or if performing the error handling requires unjustified complexity. Then:
idx = block_interf_srcu_read_lock();
if target cpumask intersects with block interference cpumask { block_interf_read_unlock(); return error }
.. ret = smp_call_function_single / stop_machine() / ... ..
block_interf_srcu_read_unlock(idx);
Regarding housekeeping flags, it is usually the case that initialization might require code execution on interference blocked CPUs (for example MTRR initialization, resctrlfs initialization, MSR writes, ...). Therefore tagging the CPUs after system initialization is necessary, which is not possible with current housekeeping flags infrastructure.
This patchset converts a few callers for demonstration purposes.
Sending the second RFC to know whether folks have objections (there were no objections to the first release), or have better ideas.
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