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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 611a9Slp1V02zJIoiWWokYWNj+3vlxet6J86XPPcScX7mR7DhPHKQesMEeIENBhStK4cpNFpwClc94gXPTisLmX5GxTL0x93hcjCpqUXRuNgwWGsO0F5r3sMlBf6thvWtbbg7i54K/E17SItQLjTKdibFK6ied6Fvxp1Vr4XEjWJ/mtYIDHWYQnbiVVHNmdOJcGRnLEAbWRfwBSPgDazVojkLYOriksfid6ehvSscGMdvHOkMfIz4hIKw7hDl0mWmAMX86o2RK4wMm1WNtuORnkWEVGLIATeykl13TpEg/MdXU4wEk4fz9LTD11NERJ7wcbAAmoAdqxgtxNLSAJx3SxlJ/Tvne3yQo570a0QCGXCDV1agAjNaUXXz0kKTlHj51mXtByRORDV9D2B1IYjlbaV6YEMtVN6HwKjPc2QpnhBsO8pEhmvnWfpodMyAzTM X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Feb 2026 09:56:00.9108 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: dfaac6ad-cf9b-448a-ed6a-08de688a98b6 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: DB1PEPF000509F6.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI1PR08MB5357 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260210_015616_900103_ED321F36 X-CRM114-Status: GOOD ( 24.63 ) 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 Fri, Feb 06, 2026 at 06:42:19PM +0000, Catalin Marinas wrote: > > On Wed, Jan 21, 2026 at 07:06:17PM +0000, Yeoreum Yun wrote: > > > +#ifdef CONFIG_ARM64_LSUI > > > +static bool has_lsui(const struct arm64_cpu_capabilities *entry, int scope) > > > +{ > > > + if (!has_cpuid_feature(entry, scope)) > > > + return false; > > > + > > > + /* > > > + * A CPU that supports LSUI should also support FEAT_PAN, > > > + * so that SW_PAN handling is not required. > > > + */ > > > + if (WARN_ON(!__system_matches_cap(ARM64_HAS_PAN))) > > > + return false; > > > + > > > + return true; > > > +} > > > +#endif > > > > I still find this artificial dependency a bit strange. Maybe one doesn't > > want any PAN at all (software or hardware) and won't get LSUI either > > (it's unlikely but possible). > > We have the uaccess_ttbr0_*() calls already for !LSUI, so maybe > > structuring the macros in a way that they also take effect with LSUI. > > For futex, we could add some new functions like uaccess_enable_futex() > > which wouldn't do anything if LSUI is enabled with hw PAN. > > Hmm, I forgot that we removed CONFIG_ARM64_PAN for 7.0, so it makes it > harder to disable. Give it a try but if the macros too complicated, we > can live with the additional check in has_lsui(). > > However, for completeness, we need to check the equivalent of > !system_uses_ttbr0_pan() but probing early, something like: > > if (IS_ENABLED(CONFIG_ARM64_SW_TTBR0_PAN) && > !__system_matches_cap(ARM64_HAS_PAN)) { > pr_info_once("TTBR0 PAN incompatible with FEAT_LSUI; disabling FEAT_LSUI"); > return false; > } > > -- TBH, I'm not sure whether it's a artifical dependency or not. AFAIK, FEAT_PAN is mandatory from Armv8.1 and the FEAT_LSUI seems to implements based on the present of "FEAT_PAN". So, for a hardware which doesn't have FEAT_PAN but has FEAT_LSUI sounds like "wrong" hardware and I'm not sure whether it's right to enable FEAT_LSUI in this case. SW_PAN case is the same problem. Since If system uses SW_PAN, that means this hardware doesn't have a "FEAT_PAN" So this question seems to ultimately boil down to whether it is appropriate to allow the use of FEAT_LSUI even when FEAT_PAN is not supported. That's why I think the purpose of "has_lsui()" is not for artifical dependency but to disable for unlike case which have !FEAT_PAN and FEAT_LSUI and IMHO it's enough to check only check with "ARM64_HAS_PAN" instead of making a new function like uaccess_enable_futext(). Am I missing something? Thanks. -- Sincerely, Yeoreum Yun