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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id F1347C7EE22 for ; Wed, 10 May 2023 08:22:59 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4QGShL124Tz3fPf for ; Wed, 10 May 2023 18:22:58 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=CzmDvf3r; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=infradead.org (client-ip=2001:8b0:10b:1:d65d:64ff:fe57:4e05; helo=desiato.infradead.org; envelope-from=peterz@infradead.org; receiver=) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=desiato.20200630 header.b=CzmDvf3r; dkim-atps=neutral Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4QGSgK6Xwsz3cLr for ; Wed, 10 May 2023 18:22:03 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=1WZCLagr9yk4Cbp+6qSxxsSMmqvOctxqT3bVkNGFhnY=; b=CzmDvf3rqlZoWLTgd3FVOKNA13 am3KRsvw5dx0zZtORpSkeQixmHm2I0T/j68VXo57hz3B2sKfsZlkzT6mcIfsGM8QExy3tEBmFQg15 5knvERiYGPZKMBkmsOAK/iQ/5rtOFvAqMTYH7nFMXqdqWWfvmHjqNDYraw79BjtqAXxEKvC5IXPLi v4WkUXSf6SdYO2DxNqGoNj/9jzwXI/RVqLwvIK8H89K9xhFYfEkKkPofOod7rLsPcDYQd4FB4I+bb ncPfZdYjPCu8FZ1ut2ZqCkZjLMrUhqEHRkvEROX3xUgFItRMwb3mnY6amim7reKFoxZZ2cjlGh5hD cm+pskqQ==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1pwf2E-007PM8-2r; Wed, 10 May 2023 08:20:55 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4DA20300338; Wed, 10 May 2023 10:18:48 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2369E20B04BA2; Wed, 10 May 2023 10:18:48 +0200 (CEST) Date: Wed, 10 May 2023 10:18:48 +0200 From: Peter Zijlstra To: Hugh Dickins Subject: Re: [PATCH 21/23] x86: Allow get_locked_pte() to fail Message-ID: <20230510081848.GD83892@hirez.programming.kicks-ass.net> References: <77a5d8c-406b-7068-4f17-23b7ac53bc83@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-ia64@vger.kernel.org, David Hildenbrand , Catalin Marinas , Qi Zheng , linux-kernel@vger.kernel.org, Max Filippov , sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, Claudio Imbrenda , Will Deacon , Greg Ungerer , linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, Helge Deller , x86@kernel.org, Russell King , Matthew Wilcox , Geert Uytterhoeven , Christian Borntraeger , Alexandre Ghiti , Heiko Carstens , linux-m68k@lists.linux-m68k.org, John Paul Adrian Glaubitz , John David Anglin , Suren Baghdasaryan , linux-arm-kernel@lists.infradead.org, Chris Zankel , Michal Simek , Thomas Bogendoerfer , linux-parisc@vger.kernel.org, linux-mm@kvack.org, linux-mips@vger.kernel.org, Palmer Dabbelt , "Kirill A. Shutemov" , "Aneesh Kumar K.V" , Andrew Morton , linuxppc-dev@lists.ozlabs.org, "David S. Miller" , Mike Rapoport , Mike Kravetz Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, May 09, 2023 at 10:08:37PM -0700, Hugh Dickins wrote: > In rare transient cases, not yet made possible, pte_offset_map() and > pte_offset_map_lock() may not find a page table: handle appropriately. > > Signed-off-by: Hugh Dickins > --- > arch/x86/kernel/ldt.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c > index 525876e7b9f4..eb844549cd83 100644 > --- a/arch/x86/kernel/ldt.c > +++ b/arch/x86/kernel/ldt.c > @@ -367,8 +367,10 @@ static void unmap_ldt_struct(struct mm_struct *mm, struct ldt_struct *ldt) > > va = (unsigned long)ldt_slot_va(ldt->slot) + offset; > ptep = get_locked_pte(mm, va, &ptl); > - pte_clear(mm, va, ptep); > - pte_unmap_unlock(ptep, ptl); > + if (ptep) { > + pte_clear(mm, va, ptep); > + pte_unmap_unlock(ptep, ptl); > + } > } Ow geez, now I have to go remember how the whole PTI/LDT crud worked :/ At first glance this seems wrong; we can't just not unmap the LDT if we can't find it in a hurry. Also, IIRC this isn't in fact a regular user mapping, so it should not be subject to THP induced seizures. ... memory bubbles back ... for PTI kernels we need to map this in the user and kernel page-tables because obviously userspace needs to be able to have access to the LDT. But it is not directly acessible by userspace. It lives in the cpu_entry_area as a virtual map of the real kernel allocation, and this virtual address is used for LLDT. Modification is done through sys_modify_ldt(). I think I would feel much better if this were something like: if (!WARN_ON_ONCE(!ptep)) This really shouldn't fail and if it does, simply skipping it isn't the right thing either.