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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C2D55C433E0 for ; Fri, 31 Jul 2020 14:29:51 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 722F1206FA for ; Fri, 31 Jul 2020 14:29:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Bnmr+2CF" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 722F1206FA Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=+k68ZMKNTVEn0j9QspEI7PstRUDlSW3YO6ARNgc0ODA=; b=Bnmr+2CF8PQWCqJgAKOxQUJNp QQ8hG9TGmvWrD1SuJBu0V+AtJiJCfLPSuLJxAPtq4Ub4XZuw0u+S+IYIJthsCnwNroTfsoRVoZy2n odsDkLmsz3Hs9mCj+ergbcq6k49R8YFsbVWwf7i2W4FiXZnfiOJPdkEuzsTeGFfqZFhrmaw1PHnYH Ccqx+s8b/ia1YzZ6WTr/xMk7U14kDlfP8bwlL96Me+yuL4FKblBr2xwcpzO/3UM4RmuSpdJFqBj6A XtZJ8CatSDXcfDSPhCCh30IxRdVZPGBT7oCux2ePe2nup2hw8Ud7U8Ar17ybFsV6+pbRojz0Ej1it g5Z/UmwyA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k1W2L-0007l6-7K; Fri, 31 Jul 2020 14:29:29 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k1W2G-0007fR-Mv; Fri, 31 Jul 2020 14:29:25 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8D1A831B; Fri, 31 Jul 2020 07:29:20 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.4.61]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C2B863F66E; Fri, 31 Jul 2020 07:29:13 -0700 (PDT) Date: Fri, 31 Jul 2020 15:29:05 +0100 From: Mark Rutland To: Catalin Marinas Subject: Re: [PATCH v2 3/7] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20200731142905.GA67415@C02TD0UTHF1T.local> References: <20200727162935.31714-1-rppt@kernel.org> <20200727162935.31714-4-rppt@kernel.org> <20200730162209.GB3128@gaia> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200730162209.GB3128@gaia> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200731_102924_873739_0187A7D7 X-CRM114-Status: GOOD ( 24.04 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Zijlstra , Dave Hansen , linux-mm@kvack.org, "H. Peter Anvin" , Christopher Lameter , Idan Yaniv , Thomas Gleixner , Elena Reshetova , linux-arch@vger.kernel.org, Tycho Andersen , linux-nvdimm@lists.01.org, Will Deacon , x86@kernel.org, Matthew Wilcox , Mike Rapoport , Ingo Molnar , Michael Kerrisk , Arnd Bergmann , James Bottomley , Borislav Petkov , Alexander Viro , Andy Lutomirski , Paul Walmsley , "Kirill A. Shutemov" , Dan Williams , linux-arm-kernel@lists.infradead.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Palmer Dabbelt , linux-fsdevel@vger.kernel.org, Andrew Morton , Mike Rapoport Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Thu, Jul 30, 2020 at 05:22:10PM +0100, Catalin Marinas wrote: > On Mon, Jul 27, 2020 at 07:29:31PM +0300, Mike Rapoport wrote: > > +static int secretmem_mmap(struct file *file, struct vm_area_struct *vma) > > +{ > > + struct secretmem_ctx *ctx = file->private_data; > > + unsigned long mode = ctx->mode; > > + unsigned long len = vma->vm_end - vma->vm_start; > > + > > + if (!mode) > > + return -EINVAL; > > + > > + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0) > > + return -EINVAL; > > + > > + if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len)) > > + return -EAGAIN; > > + > > + switch (mode) { > > + case SECRETMEM_UNCACHED: > > + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > > + fallthrough; > > + case SECRETMEM_EXCLUSIVE: > > + vma->vm_ops = &secretmem_vm_ops; > > + break; > > + default: > > + return -EINVAL; > > + } > > + > > + vma->vm_flags |= VM_LOCKED; > > + > > + return 0; > > +} > > I think the uncached mapping is not the right thing for arm/arm64. First > of all, pgprot_noncached() gives us Strongly Ordered (Device memory) > semantics together with not allowing unaligned accesses. I suspect the > semantics are different on x86. > The second, more serious problem, is that I can't find any place where > the caches are flushed for the page mapped on fault. When a page is > allocated, assuming GFP_ZERO, only the caches are guaranteed to be > zeroed. Exposing this subsequently to user space as uncached would allow > the user to read stale data prior to zeroing. The arm64 > set_direct_map_default_noflush() doesn't do any cache maintenance. It's also worth noting that in a virtual machine this is liable to be either broken (with a potential loss of coherency if the host has a cacheable alias as existing KVM hosts have), or pointless (if the host uses S2FWB to upgrade Stage-1 attribues to cacheable as existing KVM hosts also have). I think that trying to avoid the data caches creates many more problems than it solves, and I don't think there's a strong justification for trying to support that on arm64 to begin with, so I'd rather entirely opt-out on supporting SECRETMEM_UNCACHED. Thanks, Mark. _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv