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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 6FFA3C2B9F7 for ; Wed, 26 May 2021 06:09:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 465DC613F6 for ; Wed, 26 May 2021 06:09:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232604AbhEZGK6 (ORCPT ); Wed, 26 May 2021 02:10:58 -0400 Received: from mga03.intel.com ([134.134.136.65]:9834 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231573AbhEZGK5 (ORCPT ); Wed, 26 May 2021 02:10:57 -0400 IronPort-SDR: fJ51qK/kXeUw55tJoZ5CGhQT8+bv6qdHEWxG5jJLAw2bGyvGQExlB3Pac8dqCzsFJjH8oz474s Bup+3HFtyw3w== X-IronPort-AV: E=McAfee;i="6200,9189,9995"; a="202427615" X-IronPort-AV: E=Sophos;i="5.82,330,1613462400"; d="scan'208";a="202427615" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 May 2021 23:09:26 -0700 IronPort-SDR: D6ePKFlh8DlgJp4lXdFPgR+RLGvecW1w7fEWB3xxqEnhw7uEZNrdy/c+cpt6uKc/h1jF0j9uSM bnEBWrzSLWGw== X-IronPort-AV: E=Sophos;i="5.82,330,1613462400"; d="scan'208";a="476775930" Received: from unknown (HELO [10.238.130.158]) ([10.238.130.158]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 May 2021 23:09:23 -0700 Subject: Re: [PATCH RFC 4/7] kvm: x86: Add new ioctls for XSAVE extension To: Sean Christopherson Cc: pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, jing2.liu@intel.com References: <20210207154256.52850-1-jing2.liu@linux.intel.com> <20210207154256.52850-5-jing2.liu@linux.intel.com> From: "Liu, Jing2" Message-ID: <920df897-56d8-1f81-7ce2-0050fb744bd7@linux.intel.com> Date: Wed, 26 May 2021 14:09:03 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 5/25/2021 5:50 AM, Sean Christopherson wrote: > On Sun, Feb 07, 2021, Jing Liu wrote: >> The static xstate buffer kvm_xsave contains the extended register >> states, but it is not enough for dynamic features with large state. >> >> Introduce a new capability called KVM_CAP_X86_XSAVE_EXTENSION to >> detect if hardware has XSAVE extension (XFD). Meanwhile, add two >> new ioctl interfaces to get/set the whole xstate using struct >> kvm_xsave_extension buffer containing both static and dynamic >> xfeatures. Reuse fill_xsave and load_xsave for both cases. >> >> Signed-off-by: Jing Liu >> --- >> arch/x86/include/uapi/asm/kvm.h | 5 +++ >> arch/x86/kvm/x86.c | 70 +++++++++++++++++++++++++-------- >> include/uapi/linux/kvm.h | 8 ++++ >> 3 files changed, 66 insertions(+), 17 deletions(-) >> >> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h >> index 89e5f3d1bba8..bf785e89a728 100644 >> --- a/arch/x86/include/uapi/asm/kvm.h >> +++ b/arch/x86/include/uapi/asm/kvm.h >> @@ -362,6 +362,11 @@ struct kvm_xsave { >> __u32 region[1024]; >> }; >> >> +/* for KVM_CAP_XSAVE_EXTENSION */ >> +struct kvm_xsave_extension { >> + __u32 region[3072]; > Fool me once, shame on you (Intel). Fool me twice, shame on me (KVM). > > As amusing as kvm_xsave_really_extended would be, the required size should be > discoverable, not hardcoded. Thanks for reviewing the patch. When looking at current kvm_xsave structure, I felt confusing about the static hardcoding of 1024 bytes, but failed to find clue for its final decision in 2010[1]. So we'd prefer to changing the way right? Please correct me if I misunderstood. > Nothing prevents a hardware vendor from inventing > a newfangled feature that requires yet more space. > As an alternative to adding a dedicated capability, can we leverage > GET_SUPPORTED_CPUID, leaf CPUID.0xD, Yes, this is a good way to avoid a dedicated capability. Thanks for the suggestion. Use 0xD.1.EBX for size of enabled xcr0|xss if supposing kvm_xsave cares both. > to enumerate the minimum required size and > state For the state, an extreme case is using an old qemu as follows, but a new kvm with more future_featureZ supported. If hardware vendor arranges one by one, it's OK to use static state like X86XSaveArea(2) and get/set between userspace and kvm because it's non-compacted. If not, the state will not correct. So far it is OK, so I'm wondering if this would be an issue for now? X86XSaveArea2 {     ...     XSaveAVX     ...     AMX_XTILE;     future_featureX;     future_featureY; } > that the new ioctl() is available if the min size is greater than 1024? > Or is that unnecessarily convoluted... To enable a dynamic size kvm_xsave2(Thanks Jim's name suggestion), if things as follows are what we might want. /* for xstate large than 1024 */ struct kvm_xsave2 {     int size; // size of the whole xstate     void *ptr; // xstate pointer } #define KVM_GET_XSAVE2   _IOW(KVMIO,  0xa4, struct kvm_xsave2) Take @size together, so KVM need not fetch 0xd.1.ebx each time or a dedicated variable. For Userspace(Qemu): struct X86XSaveArea2 {...}// new struct holding all features if 0xd.1.ebx <= sizeof(kvm_xsave)     env->xsave_buf = alloc(sizeof(kvm_xsave))     ...     ioctl(KVM_GET/SET_XSAVE, X86XSaveArea *) else     env->xsave_buf = alloc(0xd.1.ebx + sizeof(int))     ...     xsave2 = env->xsave_buf     xsave2->size = ... X86XSaveArea2 *area2 = xsave2->ptr ioctl(KVM_GET/SET_XSAVE2, xsave2) endif [1] https://lore.kernel.org/kvm/4C10AE1D.40604@redhat.com/ Thanks, Jing