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citrix.com X-MS-Exchange-CrossTenant-Network-Message-Id: 767b487c-ad9f-4bdb-44b6-08db36f3c25b X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB3623.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Apr 2023 23:07:57.2944 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: b+/bC7rl4pbbyQiALCdhosJKIP5eAgzCn6shFLn0/u4cz2MsIziGr4KMiKfqYAriJxI+UwuI+yKZB+XPIllIvcY9mr4+/MUjnZHNrc+tcrY= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR03MB5952 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/04/2023 10:58 pm, Peter Zijlstra wrote: > On Mon, Apr 03, 2023 at 10:06:01PM +0800, Lai Jiangshan wrote: >> +/* Replicate the interrupted atomic-IST-entry's CLEAR_REGS macro. */ >> +static __always_inline void replicate_clear_regs(struct pt_regs *target) >> +{ >> + target->di = 0; >> + target->si = 0; >> + target->dx = 0; >> + target->cx = 0; >> + target->ax = 0; >> + target->r8 = 0; >> + target->r9 = 0; >> + target->r10 = 0; >> + target->r11 = 0; >> + target->bx = 0; >> + target->bp = 0; >> + target->r12 = 0; >> + target->r13 = 0; >> + target->r14 = 0; >> + target->r15 = 0; >> +} > I think there's compilers smart enough to see through your attempts at > avoiding mem{set,cpy}() there Indeed.  It took a little bit of convincing (needed 4 extra registers to zero), but https://godbolt.org/z/7rvb8db66 Including Peter's other observation about speculation safety, you basically can't have any C at all before passing IBRS/UNRET/whatever else comes along in the future. Otherwise, the compiler will make you wish you'd written it in asm the first time around. ~Andrew