On Fri, Aug 15, 2025 at 04:10:59PM +0100, Yeoreum Yun wrote: > > > Like we do in mte_enable_kernel_asymm(), if the feature is not available > > > just fall back to checking both reads and writes in the chosen > > > async/sync/asymm way. You can add some pr_info() to inform the user of > > > the chosen kasan mode. It's really mostly an performance choice. > > > > But MTE_STORE_ONLY is defined as a SYSTEM_FEATURE. > > This means that when it is called from kasan_init_hw_tags_cpu(), > > the store_only mode is never set in system_capability, > > so it cannot be checked using cpus_have_cap(). > > > > Although the MTE_STORE_ONLY capability is verified by > > directly reading the ID register (seems ugly), > > my concern is the potential for an inconsistent state across CPUs. > > > > For example, in the case of ASYMM, which is a BOOT_CPU_FEATURE, > > all CPUs operate in the same mode — > > if ASYMM is not supported, either > > all CPUs run in synchronous mode, or all run in asymmetric mode. > > > > However, for MTE_STORE_ONLY, CPUs that support the feature will run in > > store-only mode, > > while those that do not will run with full checking for all operations. > > > > If we want to enable MTE_STORE_ONLY in kasan_init_hw_tags_cpu(), > > I believe it should be reclassified as a BOOT_CPU_FEATURE.x > > Otherwise, the cpu_enable_mte_store_only() function should still be called > > as the enable callback for the MTE_STORE_ONLY feature. > > In that case, kasan_enable_store_only() should be invoked (remove late > > init), > > and if it returns an error, stop_machine() should be called to disable > > the STORE_ONLY feature on all other CPUs > > if any CPU is found to lack support for MTE_STORE_ONLY. > > > > Am I missing something?
Good point. > So, IMHO like the ASYMM feature, it would be good to change > MTE_STORE_ONLY as BOOT_CPU_FEATURE. > That would makes everything as easiler and clear. Yeah, let's do this. If people mix different features, we'll revisit at that time. The asymmetric tag checking is also a boot CPU feature. -- Catalin
