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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: +w3x+wYLp5IKplMgMWmFzakF/YuwvK9E+Og7sH7f1gNGEW/umDqBjhEwFiqjSM9ni9CWh05hng5uqYfelnUjmNBZPcRWHp2C2J0KK5xKQZwFXTHMdlOPApFFjewrdMiYIwKx324/axHsGldxUKjPxzdLXlEWhSIEyVoyHa4J8yKfIEj4Dv4RPGno3+oTtrFuX+3N9KxbXB14+pxqCRNDXJQtIsbKzW07duVH9J+iddXhC2nx82cRRscgN4TKd2F5LUxK3HO4/Vv/uLiOBG8wEaaR+8u+3wcXa5h3Jo1WzRjuNiEGCIMVAt8XSbA0EebtaYE/f5WRkLZgiZ5xpDS39m1v829saY0ByuVZVHjocFquJCL9FLJIeMdZYinjN9yaAZCaQJqdlICsFFQgzd3G6l5r8oajU5zuI4Kdeuw1YDUARcy8df/mCOahUU0u3RDU X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Feb 2026 15:55:34.6803 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: edcfc1a1-211c-4ef0-4de0-08de72f3fb0e 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: DB1PEPF000509F8.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GVXPR08MB11761 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260223_075544_673571_F633B496 X-CRM114-Status: GOOD ( 19.76 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Catalin, > On Tue, Feb 10, 2026 at 05:01:33PM +0000, Yeoreum Yun wrote: > > > Why not keep uaccess_enable_privileged() in > > > arch_futex_atomic_op_inuser() and cmpxchg for all cases and make it a > > > no-op if FEAT_LSUI is implemented together with FEAT_PAN? > > > > This is because I had a assumption FEAT_PAN must be present > > when FEAT_LSUI is presented and this was not considering the virtualisation case. > > and FEAT_PAN is present uaccess_ttbr0_enable() becomes nop and > > following feedback you gave - https://lore.kernel.org/all/aJ9oIes7LLF3Nsp1@arm.com/ > > and the reason you mention last, It doesn't need to call mte_enable_tco(). > > > > That's why I thought it doesn't need to call uaccess_enable_privileged(). > > > > But for a compatibility with SW_PAN, I think we can put only > > uaccess_ttbr0_enable() in arch_futex_atomic_op_inuser() and cmpxchg simply > > instead of adding a new APIs uaccess_enable_futex() and > > by doing this I think has_lsui() can be removed with its WRAN. > > Yes, I think you can use uaccess_ttbr0_enable() when we take the > FEAT_LSUI path. What I meant above was for uaccess_enable_privileged() > to avoid PAN disabling if we have FEAT_LSUI as we know all cases would > be executed with user privileges. > > Either way, we don't need a new uaccess_enable_futex(). Yes. But like raw_copy_from/to_user() where use ldtr*/sttr* when MOPS isn't enabled, It seems better to use uaccess_ttbr0_enable() instead of making special handling for LSUI in uaccess_enable_privileged(). This seems more consistent since ldtr*/sttr* are similar function of LSUI (doesn't disable PAN) and doesn't enable mto. > > > > BTW, with the removal of uaccess_enable_privileged(), we now get MTE tag > > > checks for the futex operations. I think that's good as it matches the > > > other uaccess ops, though it's a slight ABI change. If we want to > > > preserve the old behaviour, we definitely need > > > uaccess_enable_privileged() that only does mte_enable_tco(). > > > > I think we don't need to preserve the old behaviour. so we can skip > > mte_enable_tco() in case of FEAT_LSUI is presented. > > Just spell it out in the commit log that we have a slight ABI change. I > don't think we'll have a problem but it needs at least checking with > some user-space (libc, Android) people. I see. Thanks! > > -- > Catalin -- Sincerely, Yeoreum Yun