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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86C00C433F5 for ; Thu, 12 May 2022 13:01:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 1D7A66B0074; Thu, 12 May 2022 09:01:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 187C96B0075; Thu, 12 May 2022 09:01:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 027706B0078; Thu, 12 May 2022 09:01:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id E7D426B0074 for ; Thu, 12 May 2022 09:01:16 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 7283531138 for ; Thu, 12 May 2022 13:01:16 +0000 (UTC) X-FDA: 79457101752.18.DECAE3F Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by imf16.hostedemail.com (Postfix) with ESMTP id 89A621800D2 for ; Thu, 12 May 2022 13:01:04 +0000 (UTC) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-308-WKnz_SfHO5SeLrhiKjvyFg-1; Thu, 12 May 2022 14:01:09 +0100 X-MC-Unique: WKnz_SfHO5SeLrhiKjvyFg-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.32; Thu, 12 May 2022 14:01:07 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.033; Thu, 12 May 2022 14:01:07 +0100 From: David Laight To: "'Kirill A. Shutemov'" , Dave Hansen , Andy Lutomirski , "Peter Zijlstra" CC: "x86@kernel.org" , Andrey Ryabinin , Alexander Potapenko , "Dmitry Vyukov" , "H . J . Lu" , Andi Kleen , Rick Edgecombe , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] x86: Implement Linear Address Masking support Thread-Topic: [PATCH] x86: Implement Linear Address Masking support Thread-Index: AQHYZN7+/opgI73BZUKmGdIzOSRkmq0bNCgQ Date: Thu, 12 May 2022 13:01:07 +0000 Message-ID: References: <20220511022751.65540-1-kirill.shutemov@linux.intel.com> <20220511022751.65540-2-kirill.shutemov@linux.intel.com> In-Reply-To: <20220511022751.65540-2-kirill.shutemov@linux.intel.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 89A621800D2 X-Stat-Signature: 6hqwqueaoogucbfnpoza9913systmkmx X-Rspam-User: Authentication-Results: imf16.hostedemail.com; dkim=none; spf=pass (imf16.hostedemail.com: domain of david.laight@aculab.com designates 185.58.85.151 as permitted sender) smtp.mailfrom=david.laight@aculab.com; dmarc=pass (policy=none) header.from=aculab.com X-HE-Tag: 1652360464-512952 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Kirill A. Shutemov > Sent: 11 May 2022 03:28 >=20 > Linear Address Masking feature makes CPU ignore some bits of the virtual > address. These bits can be used to encode metadata. >=20 > The feature is enumerated with CPUID.(EAX=3D07H, ECX=3D01H):EAX.LAM[bit 2= 6]. >=20 > CR3.LAM_U57[bit 62] allows to encode 6 bits of metadata in bits 62:57 of > user pointers. >=20 > CR3.LAM_U48[bit 61] allows to encode 15 bits of metadata in bits 62:48 > of user pointers. >=20 > CR4.LAM_SUP[bit 28] allows to encode metadata of supervisor pointers. > If 5-level paging is in use, 6 bits of metadata can be encoded in 62:57. > For 4-level paging, 15 bits of metadata can be encoded in bits 62:48. >=20 ... > +static vaddr clean_addr(CPUArchState *env, vaddr addr) > +{ > + CPUClass *cc =3D CPU_GET_CLASS(env_cpu(env)); > + > + if (cc->tcg_ops->do_clean_addr) { > + addr =3D cc->tcg_ops->do_clean_addr(env_cpu(env), addr); The performance of a conditional indirect call will be horrid. Over-engineered when there is only one possible function. .... > + > +static inline int64_t sign_extend64(uint64_t value, int index) > +{ > + int shift =3D 63 - index; > + return (int64_t)(value << shift) >> shift; > +} Shift of signed integers are UB. > +vaddr x86_cpu_clean_addr(CPUState *cs, vaddr addr) > +{ > + CPUX86State *env =3D &X86_CPU(cs)->env; > + bool la57 =3D env->cr[4] & CR4_LA57_MASK; > + > + if (addr >> 63) { > + if (env->cr[4] & CR4_LAM_SUP) { > + return sign_extend64(addr, la57 ? 56 : 47); > + } > + } else { > + if (env->cr[3] & CR3_LAM_U57) { > + return sign_extend64(addr, 56); > + } else if (env->cr[3] & CR3_LAM_U48) { > + return sign_extend64(addr, 47); > + } > + } That is completely horrid. Surely it can be just: =09if (addr && 1u << 63) =09=09return addr | env->address_mask; =09else =09=09return addr & ~env->address_mask; Where 'address_mask' is 0x7ff.... although since you really want a big gap between valid user and valid kernel addresses allowing masked kernel addresses adds costs elsewhere. I've no idea how often the address masking is required? Hopefully almost never? copy_to/from_user() (etc) need to be able to use user addresses without having to mask them. =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)