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=-15.7 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,URIBL_BLOCKED, 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 4D5DAC2B9F4 for ; Mon, 14 Jun 2021 19:34:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3B73A61185 for ; Mon, 14 Jun 2021 19:34:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235168AbhFNTgq (ORCPT ); Mon, 14 Jun 2021 15:36:46 -0400 Received: from mga05.intel.com ([192.55.52.43]:19852 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235138AbhFNTgl (ORCPT ); Mon, 14 Jun 2021 15:36:41 -0400 IronPort-SDR: sJLJS6vHOrBj8iksW0hv1PPXxuB4l+yN+wndkUFSyewUqVLZGomEtO2penzMoBffWIlcPg14Yd n7toOn7xbptA== X-IronPort-AV: E=McAfee;i="6200,9189,10015"; a="291500757" X-IronPort-AV: E=Sophos;i="5.83,273,1616482800"; d="scan'208";a="291500757" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jun 2021 12:34:34 -0700 IronPort-SDR: ynXsLDiELkRBmy6o8C2rIHhBfVbA7UJnfXSVUsVsMI4R4yNKxnPcN5DJhAM8pMmk9mcR8kntBV s6x6hF3UbxWg== X-IronPort-AV: E=Sophos;i="5.83,273,1616482800"; d="scan'208";a="451695454" Received: from sukulkar-mobl1.amr.corp.intel.com (HELO [10.212.204.222]) ([10.212.204.222]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jun 2021 12:34:33 -0700 Subject: Re: [patch 09/41] x86/kvm: Avoid looking up PKRU in XSAVE buffer To: Borislav Petkov , Thomas Gleixner Cc: LKML , Andy Lutomirski , Dave Hansen , Fenghua Yu , Tony Luck , Yu-cheng Yu , Sebastian Andrzej Siewior , Peter Zijlstra , Kan Liang References: <20210611161523.508908024@linutronix.de> <20210611163111.931697147@linutronix.de> 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: multipart/mixed; boundary="------------4C51F0A24FF5C92C6F645E04" Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------4C51F0A24FF5C92C6F645E04 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit On 6/14/21 3:26 AM, Borislav Petkov wrote: > On Fri, Jun 11, 2021 at 06:15:32PM +0200, Thomas Gleixner wrote: >> - if (src) { >> - u32 size, offset, ecx, edx; >> - cpuid_count(XSTATE_CPUID, xfeature_nr, >> - &size, &offset, &ecx, &edx); >> - if (xfeature_nr == XFEATURE_PKRU) >> - memcpy(dest + offset, &vcpu->arch.pkru, >> - sizeof(vcpu->arch.pkru)); >> - else >> - memcpy(dest + offset, src, size); >> + cpuid_count(XSTATE_CPUID, xfeature_nr, >> + &size, &offset, &ecx, &edx); >> >> + if (xfeature_nr == XFEATURE_PKRU) { >> + memcpy(dest + offset, &vcpu->arch.pkru, >> + sizeof(vcpu->arch.pkru)); >> + } else { >> + src = get_xsave_addr(xsave, xfeature_nr); >> + if (src) >> + memcpy(dest + offset, src, size); >> } >> >> valid -= xfeature_mask; > > How about pulling up that PKRU case even further (pasting the whole > changed loop instead of an unreadable diff) and keeping the CPUID access > and the xsave address handling separate? > > valid = xstate_bv & ~XFEATURE_MASK_FPSSE; > while (valid) { > u32 size, offset, ecx, edx; > u64 xfeature_mask = valid & -valid; > int xfeature_nr = fls64(xfeature_mask) - 1; > void *src; > > if (xfeature_nr == XFEATURE_PKRU) { > memcpy(dest + offset, &vcpu->arch.pkru, sizeof(vcpu->arch.pkru)); > continue; > } > > cpuid_count(XSTATE_CPUID, xfeature_nr, &size, &offset, &ecx, &edx); > > src = get_xsave_addr(xsave, xfeature_nr); > if (src) > memcpy(dest + offset, src, size); > > valid -= xfeature_mask; > } I gave that a shot. Two wrinkles: The PKRU memcpy() needs 'offset' from cpuid_count() and the PKRU case also needs the 'valid -=' manipulation. The result is attached, and while it makes the diff look better, I don't think the resulting code is an improvement. > Btw, I'm wondering if that CPUID read in a loop can be replaced with > adding accessors for xstate_{offsets,sizes,..} etc and providing them to > kvm... I *think* these are already stored in xfeature_uncompacted_offset[]. It would be a pretty simple matter to export it. I just assumed that this is a slow enough path that the KVM folks don't care. >> @@ -4632,18 +4633,20 @@ static void load_xsave(struct kvm_vcpu * >> */ >> valid = xstate_bv & ~XFEATURE_MASK_FPSSE; >> while (valid) { >> + u32 size, offset, ecx, edx; >> u64 xfeature_mask = valid & -valid; >> int xfeature_nr = fls64(xfeature_mask) - 1; >> - void *dest = get_xsave_addr(xsave, xfeature_nr); >> >> - if (dest) { >> - u32 size, offset, ecx, edx; >> - cpuid_count(XSTATE_CPUID, xfeature_nr, >> - &size, &offset, &ecx, &edx); >> - if (xfeature_nr == XFEATURE_PKRU) >> - memcpy(&vcpu->arch.pkru, src + offset, >> - sizeof(vcpu->arch.pkru)); >> - else >> + cpuid_count(XSTATE_CPUID, xfeature_nr, >> + &size, &offset, &ecx, &edx); >> + >> + if (xfeature_nr == XFEATURE_PKRU) { >> + memcpy(&vcpu->arch.pkru, src + offset, >> + sizeof(vcpu->arch.pkru)); >> + } else { >> + void *dest = get_xsave_addr(xsave, xfeature_nr); >> + > > > ^ Superfluous newline. I'm happy to change it, but I usually like to separate declarations from pure code. Although, I guess that's a bit inconsistent in that file. --------------4C51F0A24FF5C92C6F645E04 Content-Type: text/x-patch; charset=UTF-8; name="pkrukvm.patch" Content-Transfer-Encoding: quoted-printable Content-Disposition: attachment; filename="pkrukvm.patch" commit a761b0a48fb62429bd98c9a1275ef3ce33f9925a Author: Dave Hansen Date: Thu Jun 3 16:08:12 2021 -0700 x86/kvm: Avoid looking up PKRU in XSAVE buffer =20 PKRU is being removed from the kernel XSAVE/FPU buffers. This remova= l will probably include warnings for code that look up PKRU in those buffers. =20 KVM currently looks up the location of PKRU but doesn't even use the pointer that it gets back. Rework the code to avoid calling get_xsave_addr() except in cases where its result is actually used. =20 This makes the code more clear and also avoids the inevitable PKRU warnings. =20 This is probably a good cleanup and could go upstream idependently of any PKRU rework. =20 Signed-off-by: Dave Hansen Signed-off-by: Thomas Gleixner =20 -- diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index b594275d49b5..ed4c3d90a18b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4589,20 +4589,21 @@ static void fill_xsave(u8 *dest, struct kvm_vcpu = *vcpu) */ valid =3D xstate_bv & ~XFEATURE_MASK_FPSSE; while (valid) { + u32 size, offset, ecx, edx; u64 xfeature_mask =3D valid & -valid; int xfeature_nr =3D fls64(xfeature_mask) - 1; - void *src =3D get_xsave_addr(xsave, xfeature_nr); - - if (src) { - u32 size, offset, ecx, edx; - cpuid_count(XSTATE_CPUID, xfeature_nr, - &size, &offset, &ecx, &edx); - if (xfeature_nr =3D=3D XFEATURE_PKRU) - memcpy(dest + offset, &vcpu->arch.pkru, - sizeof(vcpu->arch.pkru)); - else - memcpy(dest + offset, src, size); + void *src; + + cpuid_count(XSTATE_CPUID, xfeature_nr, + &size, &offset, &ecx, &edx); =20 + if (xfeature_nr =3D=3D XFEATURE_PKRU) { + memcpy(dest + offset, &vcpu->arch.pkru, + sizeof(vcpu->arch.pkru)); + } else { + src =3D get_xsave_addr(xsave, xfeature_nr); + if (src) + memcpy(dest + offset, src, size); } =20 valid -=3D xfeature_mask; @@ -4632,18 +4633,20 @@ static void load_xsave(struct kvm_vcpu *vcpu, u8 = *src) */ valid =3D xstate_bv & ~XFEATURE_MASK_FPSSE; while (valid) { + u32 size, offset, ecx, edx; u64 xfeature_mask =3D valid & -valid; int xfeature_nr =3D fls64(xfeature_mask) - 1; - void *dest =3D get_xsave_addr(xsave, xfeature_nr); - - if (dest) { - u32 size, offset, ecx, edx; - cpuid_count(XSTATE_CPUID, xfeature_nr, - &size, &offset, &ecx, &edx); - if (xfeature_nr =3D=3D XFEATURE_PKRU) - memcpy(&vcpu->arch.pkru, src + offset, - sizeof(vcpu->arch.pkru)); - else + + cpuid_count(XSTATE_CPUID, xfeature_nr, + &size, &offset, &ecx, &edx); + + if (xfeature_nr =3D=3D XFEATURE_PKRU) { + memcpy(&vcpu->arch.pkru, src + offset, + sizeof(vcpu->arch.pkru)); + } else { + void *dest =3D get_xsave_addr(xsave, xfeature_nr); + + if (dest) memcpy(dest, src + offset, size); } =20 --------------4C51F0A24FF5C92C6F645E04--