From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B4C6ACFC295 for ; Fri, 21 Nov 2025 17:37:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 11FAC6B008C; Fri, 21 Nov 2025 12:37:22 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0F7EA6B0093; Fri, 21 Nov 2025 12:37:22 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F28976B0095; Fri, 21 Nov 2025 12:37:21 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id E27DF6B008C for ; Fri, 21 Nov 2025 12:37:21 -0500 (EST) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 89FA51300A1 for ; Fri, 21 Nov 2025 17:37:21 +0000 (UTC) X-FDA: 84135320682.26.73852EB Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf04.hostedemail.com (Postfix) with ESMTP id DC2CA40017 for ; Fri, 21 Nov 2025 17:37:17 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=HLyGab2g; spf=pass (imf04.hostedemail.com: domain of vschneid@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=vschneid@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1763746639; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=V3OE0zpMaGFe7FLO1SjE8KbYNBSyHZmUa+LcldBnwuQ=; b=ruH+o9oTWB4R9RcB8UfA9Y2Alr/5K8HJ8PYKVEbusTvQSk7eFYsYeiDenu1iCe27hmymTa kU/88MBSPeaP6j5MvxaEDyhi/hOvIqkturX1smKO/LCKNwaZddR///BXUsstmiT/5kPTu0 +/l5gauXuUFAuw/LWqLb3kPDMUX419I= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=HLyGab2g; spf=pass (imf04.hostedemail.com: domain of vschneid@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=vschneid@redhat.com; dmarc=pass (policy=quarantine) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1763746639; a=rsa-sha256; cv=none; b=uTtlpz5+r8prl0iSXpQo/tz5s/SXkNUTscCrOw0uoEwe1JllsctUDOiIy3KGwimP9NkYg4 poSawWkchFosMwGPL6je8PmN+su1FWene9ucnPTJdnK0o9wWojk0SYK+1hZJf3Hl42fn1d QKXvEYchSbzo1xVb55w+PvNQhOm5tTQ= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1763746637; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=V3OE0zpMaGFe7FLO1SjE8KbYNBSyHZmUa+LcldBnwuQ=; b=HLyGab2gL8y2QKkizA/AljoznHmN75jEWMrWhCPWYV136R0boKIzdyjJoPMCydKrzxz7ND CermfLPBAoqEbP2yR1BuEqEtBB/fxSlKGblSUXUmdPMN/43PHZHXjlO7HVyBQDRNQ5K1ev pEU0sk2Lkjw7BavCgB3h2gZ/nkpSiiY= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-332-xcydoKdWOhawG3kY_StUFg-1; Fri, 21 Nov 2025 12:37:13 -0500 X-MC-Unique: xcydoKdWOhawG3kY_StUFg-1 X-Mimecast-MFC-AGG-ID: xcydoKdWOhawG3kY_StUFg_1763746632 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-429c5c8ae3bso1940054f8f.0 for ; Fri, 21 Nov 2025 09:37:13 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1763746632; x=1764351432; h=mime-version:message-id:date:references:in-reply-to:subject:cc:to :from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=V3OE0zpMaGFe7FLO1SjE8KbYNBSyHZmUa+LcldBnwuQ=; b=akFICloSAMbKlKcJd6mf14CIN3yspO2n1ssnPWqgIBwrfw0rl7jEIS70I/7of5Ovy8 qB8NXMRO7qvzMlh2idrgEvIIq8UORbOW4Ry4k2DBka2OR4WnYY33dOpeTwvVcCrDl+5E JQsVEbfa6ZpXvdS2tVNDqV5BGZLJcfjpnuabLudbQXdGWfggIJfHtTMQSrg+FFuktNNH W//kSaFG9F7183Kt6mVavwtYXY9QPM8o9+gO1EDdAeCr7bmWNXV4TnkPuYSNwAOovl6i aUX5AexUaWjCER79S0+0RDZkt7ACCw37JEJGQ8lMq26DaZ7VaQl7Sz56LzUe17Dpw1BR 1Opg== X-Forwarded-Encrypted: i=1; AJvYcCWV5K9yzbGE8GdFJdhJCL6a451Gez/3uQucEqu/SMKHedSAUn8ApTF3UdqSbZ9llh4b9kJNgzKFug==@kvack.org X-Gm-Message-State: AOJu0YyAZfLaNMOOGycNz7pu8ZpZa7Aiwutw52jPA079Iw6fh6MCPl5i ULHcS593yqN559dbXzHZBAEpsxzU6CKERc95VJwE6Bksf2w9O5SF7MMGagDSZLLHwrQYA0vlwAS xW7+6GgF/X2bj3vbKHb+3He7UvPCKQiAL6nvzqVQueS0TxYPx6oO9 X-Gm-Gg: ASbGnct7+H5MPct5ffPHg+3hnd4OYR0Ehroz/WoqRFunHP6c3TtokK2VYDRCjbG0GqV 8nZdIvj1TkwDC/GMLOzkyhW81BYWhMKEAjryc82EmLTuWpu8kJhP+WBpaRdB/o/Q87rLsnbCsnO dC9TeYALNr/v1g4sbCbZJhuXTcuOxBOtAu/uyjZiRR/o2dsSuXQiOjckuklkFdDfEfBzxtSOzcR jHbaKzQWHMREzshDCtlyrtDjnmRvOmDLLXLsEp3I9QFSFxAxIcge4Mcx+irdjdXFZmBafgZfYdN NJdSN2iwVgW+vKx9cqHuc9SqgXXwRLCb4qdLjSn21nZ019TY743g7sN1+CYeW6pzeD5D/XwDNeq N9Rezc9Mo91lH/vmm+Fs9rRvzmZa0VvatiiZdyULMCOdOqHGenkrs74jVXfdPucHqCy4Rj3Y= X-Received: by 2002:a05:6000:2282:b0:42b:3ab7:b8b9 with SMTP id ffacd0b85a97d-42cc1cbd0dcmr3334302f8f.20.1763746632029; Fri, 21 Nov 2025 09:37:12 -0800 (PST) X-Google-Smtp-Source: AGHT+IFwrptJrvQrMlATO+zOU3GD53XUKYoEIwVBRtwZMVM9uxcxDwDk+rU+CpbkpyNs1Ksl4qe7Bg== X-Received: by 2002:a05:6000:2282:b0:42b:3ab7:b8b9 with SMTP id ffacd0b85a97d-42cc1cbd0dcmr3334227f8f.20.1763746631366; Fri, 21 Nov 2025 09:37:11 -0800 (PST) Received: from vschneid-thinkpadt14sgen2i.remote.csb (213-44-135-146.abo.bbox.fr. [213.44.135.146]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42cc231dc6esm4094867f8f.7.2025.11.21.09.37.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Nov 2025 09:37:10 -0800 (PST) From: Valentin Schneider To: Dave Hansen , linux-kernel@vger.kernel.org, linux-mm@kvack.org, rcu@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev, linux-riscv@lists.infradead.org, linux-arch@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Arnaldo Carvalho de Melo , Josh Poimboeuf , Paolo Bonzini , Arnd Bergmann , Frederic Weisbecker , "Paul E. McKenney" , Jason Baron , Steven Rostedt , Ard Biesheuvel , Sami Tolvanen , "David S. Miller" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki , Mathieu Desnoyers , Mel Gorman , Andrew Morton , Masahiro Yamada , Han Shen , Rik van Riel , Jann Horn , Dan Carpenter , Oleg Nesterov , Juri Lelli , Clark Williams , Yair Podemsky , Marcelo Tosatti , Daniel Wagner , Petr Tesarik , Shrikanth Hegde Subject: Re: [RFC PATCH v7 30/31] x86/mm, mm/vmalloc: Defer kernel TLB flush IPIs under CONFIG_COALESCE_TLBI=y In-Reply-To: References: <20251114150133.1056710-1-vschneid@redhat.com> <20251114151428.1064524-10-vschneid@redhat.com> Date: Fri, 21 Nov 2025 18:37:09 +0100 Message-ID: MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: LOY9KTpbaPu4r3FPYKXQDXFfb40k9n8GGaIUONWTIEw_1763746632 X-Mimecast-Originator: redhat.com Content-Type: text/plain X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: DC2CA40017 X-Stat-Signature: suro17o9nbjtut58oom5pdn6tiazt4qy X-Rspam-User: X-HE-Tag: 1763746637-412215 X-HE-Meta: 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 9W3cFMgI wwyIVaUyU/kv3RBYjO1DPaGcCXH/LkwmJSRXnaHnlcH+5A0EFdChfnI1ClUzyk1iXwQzeO/8Go5YlQ0sHgoeE5qQpLHoflBRIVaV9i8l/Eoe63OAUf6QK+bYy47oKQDQWfM6kyv77qfxTyFcpCjKI47Bck+f+YNZ0x9RusyIlxlWGJU6RQu066TSj5Me4sgew2SAHsQhndxiTjvljU9hv6SbhPrJsouRnro4FPswXV9thv/kfppsxUfGaY7Xt076KUX7HATU9PtIsI7vGhv0MAVAymwnA4pQYckZPMd0QggH8TISd/a0dYavbTM6jLcyBar+cEQ11zhkGPB3ZnFQvcOTypx1jGmnctKXn6LGbpLjARtccws370e7NFhN/rU0rYnMGRMVvXosFvcE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 19/11/25 10:31, Dave Hansen wrote: > On 11/14/25 07:14, Valentin Schneider wrote: >> +static bool flush_tlb_kernel_cond(int cpu, void *info) >> +{ >> + return housekeeping_cpu(cpu, HK_TYPE_KERNEL_NOISE) || >> + per_cpu(kernel_cr3_loaded, cpu); >> +} > > Is it OK that 'kernel_cr3_loaded' can be be stale? Since it's not part > of the instruction that actually sets CR3, there's a window between when > 'kernel_cr3_loaded' is set (or cleared) and CR3 is actually written. > > Is that OK? > > It seems like it could lead to both unnecessary IPIs being sent and for > IPIs to be missed. > So the pattern is SWITCH_TO_KERNEL_CR3 FLUSH KERNEL_CR3_LOADED := 1 KERNEL_CR3_LOADED := 0 SWITCH_TO_USER_CR3 The 0 -> 1 transition has a window between the unconditional flush and the write to 1 where a remote flush IPI may be omitted. Given that the write is immediately following the unconditional flush, that would really be just two flushes racing with each other, but I could punt the kernel_cr3_loaded write above the unconditional flush. The 1 -> 0 transition is less problematic, worst case a remote flush races with the CPU returning to userspace and it'll get interrupted back to kernelspace.