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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 74875C11F68 for ; Fri, 2 Jul 2021 17:46:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 449FA61353 for ; Fri, 2 Jul 2021 17:46:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230131AbhGBRtP (ORCPT ); Fri, 2 Jul 2021 13:49:15 -0400 Received: from mga06.intel.com ([134.134.136.31]:10794 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229812AbhGBRtO (ORCPT ); Fri, 2 Jul 2021 13:49:14 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10033"; a="269895263" X-IronPort-AV: E=Sophos;i="5.83,319,1616482800"; d="scan'208";a="269895263" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jul 2021 10:46:42 -0700 X-IronPort-AV: E=Sophos;i="5.83,319,1616482800"; d="scan'208";a="409569809" Received: from tkhalx-mobl.amr.corp.intel.com (HELO [10.252.132.13]) ([10.252.132.13]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Jul 2021 10:46:41 -0700 Subject: Re: [PATCH v6-fix 06/26] x86/fpu/xstate: Calculate and remember dynamic XSTATE buffer sizes To: "Chang S. Bae" , bp@suse.de, luto@kernel.org, tglx@linutronix.de, mingo@kernel.org, x86@kernel.org Cc: len.brown@intel.com, jing2.liu@intel.com, ravi.v.shankar@intel.com, linux-kernel@vger.kernel.org References: <7B6BF36A-E1C5-4D7C-96EC-2036AE27414B@intel.com> <20210702151726.27293-1-chang.seok.bae@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzShEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gPGRhdmVAc3I3MS5uZXQ+wsF7BBMBAgAlAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAUCTo3k0QIZAQAKCRBoNZUwcMmSsMO2D/421Xg8pimb9mPzM5N7khT0 2MCnaGssU1T59YPE25kYdx2HntwdO0JA27Wn9xx5zYijOe6B21ufrvsyv42auCO85+oFJWfE K2R/IpLle09GDx5tcEmMAHX6KSxpHmGuJmUPibHVbfep2aCh9lKaDqQR07gXXWK5/yU1Dx0r VVFRaHTasp9fZ9AmY4K9/BSA3VkQ8v3OrxNty3OdsrmTTzO91YszpdbjjEFZK53zXy6tUD2d e1i0kBBS6NLAAsqEtneplz88T/v7MpLmpY30N9gQU3QyRC50jJ7LU9RazMjUQY1WohVsR56d ORqFxS8ChhyJs7BI34vQusYHDTp6PnZHUppb9WIzjeWlC7Jc8lSBDlEWodmqQQgp5+6AfhTD kDv1a+W5+ncq+Uo63WHRiCPuyt4di4/0zo28RVcjtzlGBZtmz2EIC3vUfmoZbO/Gn6EKbYAn rzz3iU/JWV8DwQ+sZSGu0HmvYMt6t5SmqWQo/hyHtA7uF5Wxtu1lCgolSQw4t49ZuOyOnQi5 f8R3nE7lpVCSF1TT+h8kMvFPv3VG7KunyjHr3sEptYxQs4VRxqeirSuyBv1TyxT+LdTm6j4a mulOWf+YtFRAgIYyyN5YOepDEBv4LUM8Tz98lZiNMlFyRMNrsLV6Pv6SxhrMxbT6TNVS5D+6 UorTLotDZKp5+M7BTQRUY85qARAAsgMW71BIXRgxjYNCYQ3Xs8k3TfAvQRbHccky50h99TUY sqdULbsb3KhmY29raw1bgmyM0a4DGS1YKN7qazCDsdQlxIJp9t2YYdBKXVRzPCCsfWe1dK/q 66UVhRPP8EGZ4CmFYuPTxqGY+dGRInxCeap/xzbKdvmPm01Iw3YFjAE4PQ4hTMr/H76KoDbD cq62U50oKC83ca/PRRh2QqEqACvIH4BR7jueAZSPEDnzwxvVgzyeuhwqHY05QRK/wsKuhq7s UuYtmN92Fasbxbw2tbVLZfoidklikvZAmotg0dwcFTjSRGEg0Gr3p/xBzJWNavFZZ95Rj7Et db0lCt0HDSY5q4GMR+SrFbH+jzUY/ZqfGdZCBqo0cdPPp58krVgtIGR+ja2Mkva6ah94/oQN lnCOw3udS+Eb/aRcM6detZr7XOngvxsWolBrhwTQFT9D2NH6ryAuvKd6yyAFt3/e7r+HHtkU kOy27D7IpjngqP+b4EumELI/NxPgIqT69PQmo9IZaI/oRaKorYnDaZrMXViqDrFdD37XELwQ gmLoSm2VfbOYY7fap/AhPOgOYOSqg3/Nxcapv71yoBzRRxOc4FxmZ65mn+q3rEM27yRztBW9 AnCKIc66T2i92HqXCw6AgoBJRjBkI3QnEkPgohQkZdAb8o9WGVKpfmZKbYBo4pEAEQEAAcLB XwQYAQIACQUCVGPOagIbDAAKCRBoNZUwcMmSsJeCEACCh7P/aaOLKWQxcnw47p4phIVR6pVL e4IEdR7Jf7ZL00s3vKSNT+nRqdl1ugJx9Ymsp8kXKMk9GSfmZpuMQB9c6io1qZc6nW/3TtvK pNGz7KPPtaDzvKA4S5tfrWPnDr7n15AU5vsIZvgMjU42gkbemkjJwP0B1RkifIK60yQqAAlT YZ14P0dIPdIPIlfEPiAWcg5BtLQU4Wg3cNQdpWrCJ1E3m/RIlXy/2Y3YOVVohfSy+4kvvYU3 lXUdPb04UPw4VWwjcVZPg7cgR7Izion61bGHqVqURgSALt2yvHl7cr68NYoFkzbNsGsye9ft M9ozM23JSgMkRylPSXTeh5JIK9pz2+etco3AfLCKtaRVysjvpysukmWMTrx8QnI5Nn5MOlJj 1Ov4/50JY9pXzgIDVSrgy6LYSMc4vKZ3QfCY7ipLRORyalFDF3j5AGCMRENJjHPD6O7bl3Xo 4DzMID+8eucbXxKiNEbs21IqBZbbKdY1GkcEGTE7AnkA3Y6YB7I/j9mQ3hCgm5muJuhM/2Fr OPsw5tV/LmQ5GXH0JQ/TZXWygyRFyyI2FqNTx4WHqUn3yFj8rwTAU1tluRUYyeLy0ayUlKBH ybj0N71vWO936MqP6haFERzuPAIpxj2ezwu0xb1GjTk4ynna6h5GjnKgdfOWoRtoWndMZxbA z5cecg== Message-ID: Date: Fri, 2 Jul 2021 10:46:39 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210702151726.27293-1-chang.seok.bae@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/2/21 8:17 AM, Chang S. Bae wrote: > The XSTATE per-task buffer is currently embedded into struct fpu with > static size. To accommodate dynamic user XSTATEs, record the maximum and > minimum buffer sizes. > > Rename the size calculation function. It calculates the maximum XSTATE size > and sanity checks it with CPUID. It also calculates the static embedded > buffer size by excluding the dynamic user states from the maximum size. This is missing a few things for me. I'd probably start with this instead: The CPUID instruction separately enumerates sizes and alignments of individual xfeatures. It independently enumerates the required size of an entire XSAVE buffer to store all enabled features. calculate_xstate_sizes() currently uses the individual feature size/alignment enumeration to independently recalculate the required XSAVE buffer size. This is compared against the CPUID- provided value. Dynamic xstates introduce another wrinkle: with them, the 'struct fpu' buffer no longer contains all of the enabled state components. This means that there are now two separate sizes: 1. The CPUID-enumerated all-feature "maxmimum" size 2. The size of the 'struct fpu' inline buffer ... then go on to explain how you added the #2 calculations > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c > index e03853bb2603..75969f1ef4b3 100644 > --- a/arch/x86/kernel/fpu/xstate.c > +++ b/arch/x86/kernel/fpu/xstate.c > @@ -590,24 +590,36 @@ static void check_xstate_against_struct(int nr) > } > } > > -/* > - * This essentially double-checks what the cpu told us about > - * how large the XSAVE buffer needs to be. We are recalculating > - * it to be safe. > +/** > + * calculate_xstate_sizes() - Calculate the xstate per-task buffer sizes. > + * > + * Record the minimum and double-check the maximum against what the CPU > + * told. > * > * Independent XSAVE features allocate their own buffers and are not > * covered by these checks. Only the size of the buffer for task->fpu > * is checked here. > + * > + * Dynamic user states are stored in this per-task buffer. They account > + * for the delta between the maximum and the minimum. > + * > + * Return: nothing. > */ I'm not sure "Return: nothing" is worth saying. The "void" kinda gives it away. > -static void do_extra_xstate_size_checks(void) > +static void calculate_xstate_sizes(void) > { > - int paranoid_xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE; > - int i; > + int xstate_size = FXSAVE_SIZE + XSAVE_HDR_SIZE; > + int xstate_size_no_dynamic, i; Both the changelog and the function description talk about the maximum and minimum sizes of the xsave buffer. Unfortunately, that doesn't seem to be reflected in the naming at all. > + xstate_size_no_dynamic = xstate_size; > > for (i = FIRST_EXTENDED_XFEATURE; i < XFEATURE_MAX; i++) { > + bool user_dynamic; > + > if (!xfeature_enabled(i)) > continue; > > + user_dynamic = (xfeatures_mask_user_dynamic & BIT_ULL(i)) ? true : false; > + > check_xstate_against_struct(i); > /* > * Supervisor state components can be managed only by > @@ -617,27 +629,39 @@ static void do_extra_xstate_size_checks(void) > XSTATE_WARN_ON(xfeature_is_supervisor(i)); > > /* Align from the end of the previous feature */ > - if (xfeature_is_aligned(i)) > - paranoid_xstate_size = ALIGN(paranoid_xstate_size, 64); > + if (xfeature_is_aligned(i)) { > + xstate_size = ALIGN(xstate_size, 64); > + if (!user_dynamic) > + xstate_size_no_dynamic = ALIGN(xstate_size_no_dynamic, 64); > + } > /* > * The offset of a given state in the non-compacted > * format is given to us in a CPUID leaf. We check > * them for being ordered (increasing offsets) in > * setup_xstate_features(). XSAVES uses compacted format. > */ > - if (!cpu_feature_enabled(X86_FEATURE_XSAVES)) > - paranoid_xstate_size = xfeature_uncompacted_offset(i); > + if (!cpu_feature_enabled(X86_FEATURE_XSAVES)) { > + xstate_size = xfeature_uncompacted_offset(i); > + if (!user_dynamic) > + xstate_size_no_dynamic = xfeature_uncompacted_offset(i); > + } > /* > * The compacted-format offset always depends on where > * the previous state ended. > */ > - paranoid_xstate_size += xfeature_size(i); > + xstate_size += xfeature_size(i); > + if (!user_dynamic) > + xstate_size_no_dynamic += xfeature_size(i); > } I'm not a super big fan of how that loop turned out. It's trying to keep two variables in parallel. How about making calculate_xstate_sizes() *return* the xstate size, and pass 'user_dynamic' to it: /* 'false' to exclude dynamic states: */ xstate_size_min = calculate_xstate_sizes(false); /* 'true' to include dynamic states: */ xstate_size_max = calculate_xstate_sizes(true); ... then go on to do the checks. > /* > * The size accounts for all the possible states reserved in the > * per-task buffer. Check against the maximum size. > */ > - XSTATE_WARN_ON(paranoid_xstate_size != get_xstate_config(XSTATE_MAX_SIZE)); > + XSTATE_WARN_ON(xstate_size != get_xstate_config(XSTATE_MAX_SIZE)); > + > + /* Record the one without dynamic states as the minimum. */ > + set_xstate_config(XSTATE_MIN_SIZE, xstate_size_no_dynamic); > } > > > @@ -738,14 +762,11 @@ static int __init init_xstate_size(void) > */ > set_xstate_config(XSTATE_MAX_SIZE, possible_xstate_size); > > - /* Perform an extra check for the maximum size. */ > - do_extra_xstate_size_checks(); > - > /* > - * Set the minimum to be the same as the maximum. The dynamic > - * user states are not supported yet. > + * Calculate and double-check the maximum size. Calculate and record > + * the minimum size. > */ > - set_xstate_config(XSTATE_MIN_SIZE, possible_xstate_size); > + calculate_xstate_sizes(); > > /* Ensure the minimum size fits in the statically-allocated buffer: */ > if (!is_supported_xstate_size(get_xstate_config(XSTATE_MIN_SIZE))) >