On Tue, Oct 14, 2025, Valentin Schneider wrote: > On 13/10/25 17:01, Sean Christopherson wrote: > > On Fri, Oct 10, 2025, Valentin Schneider wrote: > >> Later commits will cause objtool to warn about static keys being used in > >> .noinstr sections in order to safely defer instruction patching IPIs > >> targeted at NOHZ_FULL CPUs. > >> > >> These keys are used in .noinstr code, and can be modified at runtime > >> (/proc/kernel/vmx* write). However it is not expected that they will be > >> flipped during latency-sensitive operations, and thus shouldn't be a source > >> of interference wrt the text patching IPI. > >> > >> Mark it to let objtool know not to warn about it. > > > > Can you elaborate in the changelog on what will happen if the key is toggle? > > IIUC, smp_text_poke_batch_finish() will force IPIs if noinstr code is being > > patched. > > Right! > > > Even just a small footnote like this: > > > > Note, smp_text_poke_batch_finish() never defers IPIs if noinstr code is > > being patched, i.e. this is purely about silencing objtool warnings. > > > > to make it clear that there's no bug/race being introduced. > > Good point. How about: > > """ > Later commits will cause objtool to warn about static keys being used in > .noinstr sections in order to safely defer instruction patching IPIs > targeted at NOHZ_FULL CPUs. > > The VMX keys are used in .noinstr code, and can be modified at runtime > (/proc/kernel/vmx* write). However it is not expected that they will be > flipped during latency-sensitive operations, and thus shouldn't be a source > of interference for NOHZ_FULL CPUs wrt the text patching IPI. > > Note, smp_text_poke_batch_finish() never defers IPIs if noinstr code is > being patched, i.e. this is purely to tell objtool we're okay with updates > to that key causing IPIs and to silence the associated objtool warning. > """
LGTM. With the updated changelog, Acked-by: Sean Christopherson <[email protected]>
