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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Jan 2026 14:52:21.1510 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 648504fb-0d99-4c51-278d-08de58fcae4b 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: AMS1EPF0000003F.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV2PR08MB8414 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260121_065235_433446_BD8613AC X-CRM114-Status: GOOD ( 20.14 ) 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 > On Tue, Jan 20, 2026 at 05:59:47PM +0000, Yeoreum Yun wrote: > > On second thought, while a CPU that implements LSUI is unlikely to > > support AArch32 compatibility, > > I don't think LSUI requires the absence of AArch32. > > These two are independent features (and in fact our FVP reports/supports both). > > Did you have to configure the FVP specially for this or that a "default" > configuration? > > > Given that, I'm not sure a WARN is really necessary. > > Would it be sufficient to just drop the patch for swpX instead? > > Given that the whole point of LSUI is to remove the PAN toggling, I think > we should make an effort to make sure that we don't retain PAN toggling > paths at runtime that could potentially be targetted by attackers. If we > drop the SWP emulation patch and then see that we have AArch32 at runtime, > we should forcefully disable the SWP emulation but, since we don't actually > think we're going to see this in practice, the WARN seemed simpler. TBH, I missed the FVP configuration option clusterX.max_32bit_el, which can disable AArch32 support by setting it to -1 (default: 3). Given this, I think it’s reasonable to emit a WARN when LSUI is enabled and drop the SWP emulation path under that condition. Thanks! -- Sincerely, Yeoreum Yun