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 lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3EF4AC433F5 for ; Thu, 19 May 2022 23:23:36 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.333326.557138 (Exim 4.92) (envelope-from ) id 1nrpUC-0002B7-0m; Thu, 19 May 2022 23:23:16 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 333326.557138; Thu, 19 May 2022 23:23:15 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1nrpUB-0002B0-TL; Thu, 19 May 2022 23:23:15 +0000 Received: by outflank-mailman (input) for mailman id 333326; Thu, 19 May 2022 23:23:14 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1nrpU9-0002Au-VO for xen-devel@lists.xenproject.org; Thu, 19 May 2022 23:23:14 +0000 Received: from out5-smtp.messagingengine.com (out5-smtp.messagingengine.com [66.111.4.29]) by se1-gles-sth1.inumbo.com (Halon) with ESMTPS id a4692d36-d7ca-11ec-bd2c-47488cf2e6aa; Fri, 20 May 2022 01:23:11 +0200 (CEST) Received: from compute3.internal (compute3.nyi.internal [10.202.2.43]) by mailout.nyi.internal (Postfix) with ESMTP id DEC7F5C0109 for ; Thu, 19 May 2022 19:23:07 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute3.internal (MEProxy); Thu, 19 May 2022 19:23:07 -0400 Received: by mail.messagingengine.com (Postfix) with ESMTPA for ; Thu, 19 May 2022 19:23:07 -0400 (EDT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: a4692d36-d7ca-11ec-bd2c-47488cf2e6aa DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= invisiblethingslab.com; h=cc:content-type:date:date:from:from :in-reply-to:message-id:mime-version:reply-to:sender:subject :subject:to:to; s=fm1; t=1653002587; x=1653088987; bh=zqjTFcLaia d3MqNunNtu7UVCBZfKCDjBEpQDzT8tflI=; b=kFK9casaG8C+rdIaQV4g8Zrvvk Ktc4X2r/CMTXY00nq9h7J1591clfasO5Ue4ELIwatDGGEYDKA7UJvUcnnsyumwyy T5KUYhV24Dv95fyLdLcW88KghJEYTdRjlBc/h/YOPyUQjjRhMzHisFyhgzrb3Lb7 V20xzB3nIbY4fNa3ExrNhHDtXyvhPr3OByjmik2U2hPDXfsFJ3c2DCsDkynYsIfX wnvEg3YJvRLDaloayv/Xn+VFQpKHolYfLfrBMvAIxphe6Pb1PWvZnHG2HCwoo8yR MCB6nfwDkOCETGAXMZwE4ulk4G2TDBzOZiJNwc+4mj1ns2+/1ryds10AgNDw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-type:date:date:feedback-id :feedback-id:from:from:in-reply-to:message-id:mime-version :reply-to:sender:subject:subject:to:to:x-me-proxy:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm1; t=1653002587; x= 1653088987; bh=zqjTFcLaiad3MqNunNtu7UVCBZfKCDjBEpQDzT8tflI=; b=T aK+XoUp3RwF4BOiKXulvX17c3F1SuFmDBNW2RWRwAEz/ZJuOYYyqdxQe6IwjCOlf sftmwpdBJJJW1H/5En8HHti3C8AQQS/uT3HCOrZLCF7OO4gcKbERO3qzQRVWn0gK 70eMktajrCWi4q5ixxdGRNKNKbxjU9Ku6B86tXF+2iERi9aF9LOH7dc4/6RWV6m+ DC8TKwwtgCG3fINu+TmE0v43BSUchncNhkhKAx9O4odYAOWIIFzCr2XXVIOKQ0Pq shv1HHrshsoYNjpaOix0vkw8a6f8WGhXRQlOwbdvZJsklsO6CBxE1zZ222V9MRKU cXGlzkk05Qxj+Iphh1QtQ== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvfedriedvgddvvdcutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpeffhffvuffkgggtugesghdtreertddtjeenucfhrhhomhepffgvmhhiucforghr ihgvucfqsggvnhhouhhruceouggvmhhisehinhhvihhsihgslhgvthhhihhnghhslhgrsg drtghomheqnecuggftrfgrthhtvghrnhepleejtdegjeffleevfeeuleehjefgvdefhfeh gfejgeelteegtdetjeelueeuveefnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrg hmpehmrghilhhfrhhomhepuggvmhhisehinhhvihhsihgslhgvthhhihhnghhslhgrsgdr tghomh X-ME-Proxy: Feedback-ID: iac594737:Fastmail Date: Thu, 19 May 2022 19:22:33 -0400 From: Demi Marie Obenour To: Xen developer discussion Subject: Grant operation batching Message-ID: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="L0eN+3MD/NWPHsz0" Content-Disposition: inline --L0eN+3MD/NWPHsz0 Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Date: Thu, 19 May 2022 19:22:33 -0400 From: Demi Marie Obenour To: Xen developer discussion Subject: Grant operation batching It is well known that mapping and unmapping grants is expensive, which is why blkback has persistent grants. Could this cost be mitigated by batching, and if it was, would it affect the tradeoff of memcpy() vs grant table operations? Alternatively, would there be any interest in an =E2=80=9Cunsafe=E2=80=9D m= ode for blkback that skips both the copy and the grant operations? This is obviously unsafe (hence the name!), but in many cases that unsafety does not actually matter. For instance, a Qubes dom0 can execute any shell command it wants in any Qubes VM via qvm-run. Much easier than trying to exploit some UaF or race condition =F0=9F=99=82. More generally, when t= he backend is the all-powerful dom0, trying to defend against a malicious backend is (at least in the absence of SEV-SNP or TDX) pointless, so one might as well not bother and take the free performance. --=20 Sincerely, Demi Marie Obenour (she/her/hers) Invisible Things Lab --L0eN+3MD/NWPHsz0 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEdodNnxM2uiJZBxxxsoi1X/+cIsEFAmKG0VgACgkQsoi1X/+c IsHFIw//Uh5sIZUsANcp+T81YUAzTZZV5G+V1dktrmsETESPXsVrx8FpnVr3l0Us X+0Ny717o9Xxe9xZ8ER9OtFNa6CcDreaKisCyC4jyw6wVo6N7QRNRR/EdVpIBIZl cDMC5FzIcPTOkxkYeagixHfmIN+5dtBW/pEh1N907wLYu217DNG9hnqciP2PkzvP sVsaI48HMAGe68bbxcXmhT2h4tPaB6lucpfUKLC4/7TIRkTxxuRrMQKcUfNqeA0f WfEsRP+RzYq+qvHXXoMw44rTxmX0aXu3cq7dlpQsRVXpXVLZkGxbPieN+xmdJZS8 qaIxaY+tVcHgIbjCT5V4thTYYrjfNvwOywBKintrinPXvBfj5gSSGxItrh59ypWp n5/fH6TuhOkyQrLWkULbh6ow2wOYwpq8xij7TQb3ybE3vpspR5IwyLihXN2XwN1N 7E2iTQdZ6FuIE54ch1+5q48SZT6LCxeNGoFU8I1RarT4xCu66LYS0sjeQSsMbagy 5EXE/qMm2IdLXSwCHhKajHMUZ8aZ4bWH4yAKykPpJQEKnPFSlGcllq9SUbWptPPK 4IRH4k0ZBhpCEioaQULuphOlAmZAj+CBCM2wChOfgUXnb8Xf6SUAWXQfbGmSTMyA MKUOe/85yv3e2bS4oEWD3rfMRznt8gL6D8GS2Th2QJ8Gxh3bplw= =HO26 -----END PGP SIGNATURE----- --L0eN+3MD/NWPHsz0--