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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A932C433F5 for ; Mon, 8 Nov 2021 21:13:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E81ED619E9 for ; Mon, 8 Nov 2021 21:13:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239862AbhKHVPy (ORCPT ); Mon, 8 Nov 2021 16:15:54 -0500 Received: from mga09.intel.com ([134.134.136.24]:37609 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239825AbhKHVPy (ORCPT ); Mon, 8 Nov 2021 16:15:54 -0500 X-IronPort-AV: E=McAfee;i="6200,9189,10162"; a="232169186" X-IronPort-AV: E=Sophos;i="5.87,218,1631602800"; d="scan'208";a="232169186" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Nov 2021 13:13:09 -0800 X-IronPort-AV: E=Sophos;i="5.87,218,1631602800"; d="scan'208";a="503202566" Received: from ramyapad-mobl.amr.corp.intel.com (HELO [10.212.138.81]) ([10.212.138.81]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Nov 2021 13:13:08 -0800 Subject: Re: [PATCH 3/5] Extend e820_table to hold information about memory encryption To: Martin Fernandez Cc: linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, ardb@kernel.org, dvhart@infradead.org, andy@infradead.org, gregkh@linuxfoundation.org, rafael@kernel.org, daniel.gutson@eclypsium.com, hughsient@gmail.com, alison.schofield@intel.com, alex@eclypsium.com References: <20211105212724.2640-1-martin.fernandez@eclypsium.com> <20211105212724.2640-4-martin.fernandez@eclypsium.com> <37cdad39-7616-df3d-3c8d-84d26a59b62a@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: platform-driver-x86@vger.kernel.org On 11/8/21 10:40 AM, Martin Fernandez wrote: > On 11/5/21, Dave Hansen wrote: >> On 11/5/21 2:27 PM, Martin Fernandez wrote: >>> +void __init e820__mark_regions_as_crypto_capable(u64 start, u64 size) >>> +{ >>> + int i; >>> + u64 end = start + size; >>> + >>> + for (i = 0; i < e820_table->nr_entries; i++) { >>> + struct e820_entry *const entry = &e820_table->entries[i]; >>> + >>> + if (entry->addr >= start && entry->addr + entry->size <= end) >>> + entry->crypto_capable = true; >>> + } >>> +} >> >> Looking at this in isolation, this is really tricky. I have no idea >> what this is _supposed_ to or expected to be doing. It also makes me >> wonder what happens when start/size don't line up exactly on an e820 entry. > > Do you think it's better to just add new entries, just as they are in > the EFI memmap and then let e820__update_table handle them? > > Although, as it is it's faster, the other way would be clearer in the > code (since efi_mark_e820_regions_as_crypto_capable in part 4/5 isn't > also the nicest of the functions and with this change it would be very > straightforward), but it would require one e820__update_table. Also, > it would more accurate, since if you call this with a start and size > that doesn't cover at least one e820_entry then it will do nothing. I was actually trying to make a comment about this function's lack of documentation. But, you make a good point about the alternate approach. I don't have a preference either way. >>> @@ -327,6 +343,8 @@ int __init e820__update_table(struct e820_table >>> *table) >>> unsigned long long last_addr; >>> u32 new_nr_entries, overlap_entries; >>> u32 i, chg_idx, chg_nr; >>> + bool current_crypto; >>> + bool last_crypto = false; >>> >>> /* If there's only one memory region, don't bother: */ >>> if (table->nr_entries < 2) >>> @@ -388,13 +406,17 @@ int __init e820__update_table(struct e820_table >>> *table) >>> * 1=usable, 2,3,4,4+=unusable) >>> */ >>> current_type = 0; >>> + current_crypto = false; >>> for (i = 0; i < overlap_entries; i++) { >>> + current_crypto = current_crypto || overlap_list[i]->crypto_capable; >> >> No comment, eh? >> >> This seems backwards to me. If there are overlapping region and only >> one is crypto-capable, shouldn't the whole thing become non-crypto-capable? > > The reason for that is that right now, if a region is mark as > crypto_capable is because EFI memmap says so, and again, right now > that's the only source to fill the crypto_capable value, so I have to > "believe" it. Now that I think about it, yes I should have a least put > a comment on it. My concern was if: current_crypto=0 and overlap_list[i]->crypto_capable=1 Doesn't that mean a non-crypto entry is being parsed, but current_crypto will end up as 1? >>> /* Continue building up new map based on this information: */ >>> - if (current_type != last_type || e820_nomerge(current_type)) { >>> + if (current_type != last_type || >>> + current_crypto != last_crypto || >>> + e820_nomerge(current_type)) { >>> if (last_type != 0) { >>> new_entries[new_nr_entries].size = change_point[chg_idx]->addr - >>> last_addr; >>> /* Move forward only if the new size was non-zero: */ >>> @@ -406,6 +428,9 @@ int __init e820__update_table(struct e820_table >>> *table) >>> if (current_type != 0) { >>> new_entries[new_nr_entries].addr = change_point[chg_idx]->addr; >>> new_entries[new_nr_entries].type = current_type; >>> + new_entries[new_nr_entries].crypto_capable = current_crypto; >>> + >>> + last_crypto = current_crypto; >>> last_addr = change_point[chg_idx]->addr; >>> } >>> last_type = current_type; >> >> The "current_crypto != last_crypto" checks seem to go with the >> current_type/last_type checks. I'm naively surprised that the >> last_crypto assignment wasn't paired with the last_type assignment. >> >> I kinda get the impression this was just quickly hacked in here. It >> seems like "crypto" and "type" are very closely related in how they are >> being handled. It's a shame they're not being managed in a common way. > > Yes, "crypto" and "type" seems really close, but to be honest, this > function has a very weird flow, or something that I couldn't > completely understand. After a while thinking about it I came up with > that. > > Again, this function is a pain, but I'll dedicate it some more time to > see if I can come up with something better. Please do. Like you said, there's probably more context that it would be helpful to understand.