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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Aug 2025 15:11:36.1249 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7db7fe2f-280d-4677-c312-08dddc0e07b5 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM4PEPF00027A69.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB9PR08MB7675 [...] > > > > > + * Not marked as __init as a CPU can be hot-plugged after boot. > > > + */ > > > +void kasan_late_init_hw_tags_cpu(void) > > > +{ > > > + /* > > > + * Enable stonly mode only when explicitly requested through the command line. > > > + * If system doesn't support, kasan checks all operation. > > > + */ > > > + kasan_enable_store_only(); > > > +} > > > > There's nothing late about this. We have kasan_init_hw_tags_cpu() > > already and I'd rather have it all handled via this function. It's not > > that different from how we added asymmetric support, though store-only > > is complementary to the sync vs async checking. > > > > 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? 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. -- Sincerely, Yeoreum Yun