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 803C1E6F084 for ; Fri, 1 Nov 2024 19:29:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D8B9C6B0096; Fri, 1 Nov 2024 15:29:36 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D3AD96B0098; Fri, 1 Nov 2024 15:29:36 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C031D6B0099; Fri, 1 Nov 2024 15:29:36 -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 9E2626B0096 for ; Fri, 1 Nov 2024 15:29:36 -0400 (EDT) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 4949E1C6FC1 for ; Fri, 1 Nov 2024 19:29:36 +0000 (UTC) X-FDA: 82738515216.02.DDDC891 Received: from smtp-fw-80006.amazon.com (smtp-fw-80006.amazon.com [99.78.197.217]) by imf18.hostedemail.com (Postfix) with ESMTP id 8F0771C0013 for ; Fri, 1 Nov 2024 19:29:21 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=amazon.com header.s=amazon201209 header.b=Li2m4VLo; spf=pass (imf18.hostedemail.com: domain of "prvs=028377251=derekmn@amazon.com" designates 99.78.197.217 as permitted sender) smtp.mailfrom="prvs=028377251=derekmn@amazon.com"; dmarc=pass (policy=quarantine) header.from=amazon.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1730489241; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=NjClUgMgjMVgsWcpgKIDByy4IpAOZ+8mqyCzWaNAYPY=; b=U+bjj92ByR4tPEyBFs09lNwe40YbXJ3wqVUVidljcPb/2pwqjOeeZQCIxaPtzQMRlLK4up dD/mnccT87h+4TibEZscNWEcX1U2NX3i/XN5Dqy4m5eHwjqD7JZ6tE8LVmXsUoa1wiQv6o OUJGY3liapTij3Q0ZVXwsaKYAwBK/8w= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1730489241; a=rsa-sha256; cv=none; b=fGCEpt4VIALttIGWxCsT89bYl8FjBCqYh80wdG9ieCXofzSMKn+Oq0pPtAmPvY7g9Ixr84 IfBevPZII1LPB0iMH80wPm9pBekXRicrJYCLaAc582U0eGMcRcf1DHC8CLZxocFfD+TlqK RkR4Y+rjexGwr4c158itAC6O7IKenhE= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=amazon.com header.s=amazon201209 header.b=Li2m4VLo; spf=pass (imf18.hostedemail.com: domain of "prvs=028377251=derekmn@amazon.com" designates 99.78.197.217 as permitted sender) smtp.mailfrom="prvs=028377251=derekmn@amazon.com"; dmarc=pass (policy=quarantine) header.from=amazon.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1730489374; x=1762025374; h=message-id:date:mime-version:to:cc:references:subject: from:in-reply-to:content-transfer-encoding; bh=NjClUgMgjMVgsWcpgKIDByy4IpAOZ+8mqyCzWaNAYPY=; b=Li2m4VLo4nLkI5+9FgkKIUZn1yFw7ATtWoj3FENL18JoIJ0jCt14kaMo E8NDDGdeU+IJ0kkTfsjCalKGOnpWWQl6PtGMEaM/qEGsK+2PW8yxJve6Q XRFHN8Vo4kZy3vABsCPXloQkIkdYVxpnBhtJifQHYw2ES7I9SZjEAdH6x Q=; X-IronPort-AV: E=Sophos;i="6.11,250,1725321600"; d="scan'208";a="1341371" Received: from pdx4-co-svc-p1-lb2-vlan3.amazon.com (HELO smtpout.prod.us-west-2.prod.farcaster.email.amazon.dev) ([10.25.36.214]) by smtp-border-fw-80006.pdx80.corp.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Nov 2024 19:29:33 +0000 Received: from EX19MTAUWC001.ant.amazon.com [10.0.7.35:29829] by smtpin.naws.us-west-2.prod.farcaster.email.amazon.dev [10.0.50.158:2525] with esmtp (Farcaster) id 9b6a62cb-9bef-4c52-ac7f-cb4c542891d8; Fri, 1 Nov 2024 19:29:32 +0000 (UTC) X-Farcaster-Flow-ID: 9b6a62cb-9bef-4c52-ac7f-cb4c542891d8 Received: from EX19D003UWC002.ant.amazon.com (10.13.138.169) by EX19MTAUWC001.ant.amazon.com (10.250.64.174) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1258.34; Fri, 1 Nov 2024 19:29:32 +0000 Received: from [192.168.8.242] (10.106.101.33) by EX19D003UWC002.ant.amazon.com (10.13.138.169) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1258.35; Fri, 1 Nov 2024 19:29:28 +0000 Message-ID: <71e9b2c8-0cc4-4646-88f0-7780e108e610@amazon.com> Date: Fri, 1 Nov 2024 12:29:23 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , References: Subject: Re: [RFC PATCH v3 0/6] Direct Map Removal for guest_memfd Content-Language: en-US From: "Manwaring, Derek" In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.106.101.33] X-ClientProxiedBy: EX19D042UWB003.ant.amazon.com (10.13.139.135) To EX19D003UWC002.ant.amazon.com (10.13.138.169) X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 8F0771C0013 X-Stat-Signature: bsyt4i66tpg5hed37rz94q8oi8c7dtwx X-HE-Tag: 1730489361-459610 X-HE-Meta: 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 AmC37Yvr 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.016676, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024-11-01 at 18:43+0000, Dave Hansen wrote: > On 11/1/24 11:31, Manwaring, Derek wrote: > > From that standpoint I'm still tempted to turn the question around a bit > > for the host kernel's perspective. Like if the host kernel should not > > (and indeed cannot with TDX controls in place) access guest private > > memory, why not remove it from the direct map? > > Pretend that the machine check warts aren't there. > > It costs performance and complexity, for an only theoretical gain.  This > is especially true for a VMM that's not doing a just doing confidential > guests.  You fracture the direct map to pieces forever (for now). I'm hopeful we'll navigate the complexity in a worthwhile way for the non-CoCo case. Assuming we get there and have the option to remove from direct map, users with CoCo hardware could choose if they want to do both on their host. For me that's a sensible choice, but maybe that's just me. As far as performance, are you talking about just the fracturing or something beyond that? The data Mike brought to LSFMMBPF 2023 showed the perf impact from direct map fragmentation for memfd_secret isn't "that bad" [1]. Derek [1] https://lwn.net/Articles/931406/