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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable 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 DA513C43387 for ; Sat, 22 Dec 2018 00:02:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B011021928 for ; Sat, 22 Dec 2018 00:02:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404078AbeLVAB5 (ORCPT ); Fri, 21 Dec 2018 19:01:57 -0500 Received: from mga05.intel.com ([192.55.52.43]:41421 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729993AbeLVAB5 (ORCPT ); Fri, 21 Dec 2018 19:01:57 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Dec 2018 16:01:56 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,383,1539673200"; d="scan'208";a="129875464" Received: from ncanderx-mobl.ger.corp.intel.com (HELO localhost) ([10.249.254.238]) by fmsmga004.fm.intel.com with ESMTP; 21 Dec 2018 16:01:46 -0800 Date: Sat, 22 Dec 2018 02:01:45 +0200 From: Jarkko Sakkinen To: Sean Christopherson Cc: Andy Lutomirski , Dave Hansen , X86 ML , Platform Driver , linux-sgx@vger.kernel.org, nhorman@redhat.com, npmccallum@redhat.com, "Ayoun, Serge" , shay.katz-zamir@intel.com, Haitao Huang , Andy Shevchenko , Thomas Gleixner , "Svahn, Kai" , mark.shanahan@intel.com, Suresh Siddha , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Darren Hart , Andy Shevchenko , "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" Subject: Re: [PATCH v17 18/23] platform/x86: Intel SGX driver Message-ID: <20181222000145.GA8954@linux.intel.com> References: <20181217183613.GD12491@linux.intel.com> <20181217184333.GA26920@linux.intel.com> <20181217222047.GG12491@linux.intel.com> <20181218154417.GC28326@linux.intel.com> <20181218185349.GC30082@linux.intel.com> <20181219050047.GC14295@linux.intel.com> <20181221182809.GB27371@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181221182809.GB27371@linux.intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 21, 2018 at 10:28:09AM -0800, Sean Christopherson wrote: > > Why would you want to pass EPC through user space to KVM rather than > > KVM allocating it through kernel interfaces? > > Delegating EPC management to userspace fits better with KVM's existing > memory ABI. KVM provides a single ioctl(), KVM_SET_USER_MEMORY_REGION[1], > that allows userspace to create, move, modify and delete memory regions. > > Skipping over a lot of details, there are essentially three options for > exposing EPC to a KVM guest: > > 1) Provide a dedicated KVM ioctl() to manage EPC without routing it > through KVM_SET_USER_MEMORY_REGION. > > 2) Add a flag to 'struct kvm_userspace_memory_region' that denotes an > EPC memory region and mmap() / allocate EPC in KVM. > > 3) Provide an ABI to allocate raw EPC and let userspace manage it like > any other memory region. > > Option (1) requires duplicating all of KVM_SET_USER_MEMORY_REGION's > functionality unless the ioctl() is severly restricted. > > Option (2) is an ugly abuse of KVM_SET_USER_MEMORY_REGION since the EPC > flag would have completely different semantics than all other usage of > KVM_SET_USER_MEMORY_REGION. > > Thus, option (3). OK, thank you for patience explaining this. > Probably a better question to answer is why provide the ABI through > /dev/sgx and not /dev/kvm. IMO /dev/sgx is a more logical way to > advertise support to userspace, e.g. userspace can simply check if > /dev/sgx (or /dev/sgx/epc) exists vs. probing a KVM capability. You have to understand that for a KVM non-expert like me it was really important to get the context, which you kindly gave. I have never used KVM's memory management API but now that I know how it works all of this makes perfect sense. This is not a better question but it is definitely a good follow up question :-) I don't really understand you deduction here, however. If SGX was not supported, why couldn't the hypothetical /dev/kvm functionality just return an error? For me it sounds a bit messy that KVM functionality, which is a client to the SGX functionality, places some of its functionality to the SGX core. /Jarkko