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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7C48DC982DE for ; Fri, 16 Jan 2026 17:28:35 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CD0356B0005; Fri, 16 Jan 2026 12:28:34 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C7DAA6B008A; Fri, 16 Jan 2026 12:28:34 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B56426B008C; Fri, 16 Jan 2026 12:28:34 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id A52BD6B0005 for ; Fri, 16 Jan 2026 12:28:34 -0500 (EST) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 4B609C0BEF for ; Fri, 16 Jan 2026 17:28:34 +0000 (UTC) X-FDA: 84338511348.23.70E1CB0 Received: from fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com (fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com [63.178.143.178]) by imf21.hostedemail.com (Postfix) with ESMTP id C314B1C0011 for ; Fri, 16 Jan 2026 17:28:31 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=amazon.com header.s=amazoncorp2 header.b=DrmU9FY+; spf=pass (imf21.hostedemail.com: domain of "prvs=469074ca4=kalyazin@amazon.co.uk" designates 63.178.143.178 as permitted sender) smtp.mailfrom="prvs=469074ca4=kalyazin@amazon.co.uk"; 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=1768584512; h=from:from:sender:reply-to: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=iixAuY6QcleXCDLiS0osecYXCL2wD+IcnkmdhMNMceE=; b=dJdtv/wOupm67Q109L9x25p5v9QEkdyzJSm0umEFBT7oO9tStcgXGRaFEg0mO+seFwp9O+ fGp6mGqXJDep41r5EJBlSO249qe5fbsCvAsHmfkTVvcnk3LIXZ3tF/YJ+KN5WHOGptc1Nk zo6fmKrTwebz5e3v6lxGqGDDDt8+AkY= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=amazon.com header.s=amazoncorp2 header.b=DrmU9FY+; spf=pass (imf21.hostedemail.com: domain of "prvs=469074ca4=kalyazin@amazon.co.uk" designates 63.178.143.178 as permitted sender) smtp.mailfrom="prvs=469074ca4=kalyazin@amazon.co.uk"; dmarc=pass (policy=quarantine) header.from=amazon.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1768584512; a=rsa-sha256; cv=none; b=qEtm1XSQXMc91AZMPvvVQXs8TaZLc0UU4DIQa04rInBagkIPGrgNHOFJIM7ADgJyUcwxfE J0OyO7dCeWoH4LkFQfR6JyAnUIFw8PF0w31DYq5aDFoYnThIaGi6Hm2jqcoM7S+dVMJ3Xz 7XUGcgVRmRXEg5BbIbkLywLa51/2PJQ= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazoncorp2; t=1768584511; x=1800120511; h=message-id:date:mime-version:reply-to:subject:to:cc: references:from:in-reply-to:content-transfer-encoding; bh=iixAuY6QcleXCDLiS0osecYXCL2wD+IcnkmdhMNMceE=; b=DrmU9FY+w68bbI5eLdHAfZOhUHqyM8XCloqme/HYlq5msrzbZ0imwUYO xaRCTrdNOam2tvimyxpNJePQjWXVlXNyC1qRPoVAMcJOB/BHuSLDm+S8o LOxHIEPitk/FF9ZIxnUxN4RBnW2JrjHYkxVxM9GfzTKxJhCjAMiGxmWYB Hf+IIaOKWxdlvIPLBP2FU4wFBBtSqpnTRRtAR8nsVCHJGM5b7m5+sFRNW hs7OHecg1MDnsbEyOn3hyHWqZN9ricxhW0PUN4ocmsx7DS74aid2/k0i6 m3k5TrgPbHDEhtGLgINX6cn/KnJaL1a9M0yV4f3mGBSeynvNtUd6gVsnT g==; X-CSE-ConnectionGUID: Qy9RLilmSb6mwlMCH/r26Q== X-CSE-MsgGUID: FqlFUMb2T4mzbA9VY5PHdA== X-IronPort-AV: E=Sophos;i="6.21,231,1763424000"; d="scan'208";a="7924510" Received: from ip-10-6-6-97.eu-central-1.compute.internal (HELO smtpout.naws.eu-central-1.prod.farcaster.email.amazon.dev) ([10.6.6.97]) by internal-fra-out-010.esa.eu-central-1.outbound.mail-perimeter.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Jan 2026 17:28:13 +0000 Received: from EX19MTAEUC002.ant.amazon.com [54.240.197.236:17818] by smtpin.naws.eu-central-1.prod.farcaster.email.amazon.dev [10.0.21.80:2525] with esmtp (Farcaster) id 2ee969a8-f047-4c24-83b9-0d6192b592bb; Fri, 16 Jan 2026 17:28:13 +0000 (UTC) X-Farcaster-Flow-ID: 2ee969a8-f047-4c24-83b9-0d6192b592bb Received: from EX19D005EUB003.ant.amazon.com (10.252.51.31) by EX19MTAEUC002.ant.amazon.com (10.252.51.245) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Fri, 16 Jan 2026 17:28:13 +0000 Received: from [192.168.12.13] (10.106.82.9) by EX19D005EUB003.ant.amazon.com (10.252.51.31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Fri, 16 Jan 2026 17:28:08 +0000 Message-ID: <318407ba-ecb6-4691-8911-645fb8c20250@amazon.com> Date: Fri, 16 Jan 2026 17:28:06 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v9 07/13] KVM: guest_memfd: Add flag to remove from direct map To: "Edgecombe, Rick P" , "kalyazin@amazon.co.uk" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "kernel@xen0n.name" , "kvmarm@lists.linux.dev" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "bpf@vger.kernel.org" , "loongarch@lists.linux.dev" , "linux-doc@vger.kernel.org" CC: "david@kernel.org" , "svens@linux.ibm.com" , "catalin.marinas@arm.com" , "palmer@dabbelt.com" , "jgross@suse.com" , "surenb@google.com" , "vbabka@suse.cz" , "riel@surriel.com" , "pfalcato@suse.de" , "x86@kernel.org" , "rppt@kernel.org" , "thuth@redhat.com" , "borntraeger@linux.ibm.com" , "maz@kernel.org" , "peterx@redhat.com" , "ast@kernel.org" , "Annapurve, Vishal" , "pjw@kernel.org" , "alex@ghiti.fr" , "dave.hansen@linux.intel.com" , "tglx@linutronix.de" , "hca@linux.ibm.com" , "willy@infradead.org" , "wyihan@google.com" , "ryan.roberts@arm.com" , "yang@os.amperecomputing.com" , "jolsa@kernel.org" , "jmattson@google.com" , "luto@kernel.org" , "aneesh.kumar@kernel.org" , "haoluo@google.com" , "patrick.roy@linux.dev" , "akpm@linux-foundation.org" , "coxu@redhat.com" , "mhocko@suse.com" , "mlevitsk@redhat.com" , "jgg@ziepe.ca" , "hpa@zytor.com" , "song@kernel.org" , "Liam.Howlett@oracle.com" , "maobibo@loongson.cn" , "peterz@infradead.org" , "oupton@kernel.org" , "lorenzo.stoakes@oracle.com" , "jhubbard@nvidia.com" , "martin.lau@linux.dev" , "jthoughton@google.com" , "Jonathan.Cameron@huawei.com" , "Yu, Yu-cheng" , "eddyz87@gmail.com" , "yonghong.song@linux.dev" , "chenhuacai@kernel.org" , "shuah@kernel.org" , "prsampat@amd.com" , "kevin.brodsky@arm.com" , "shijie@os.amperecomputing.com" , "itazur@amazon.co.uk" , "suzuki.poulose@arm.com" , "pbonzini@redhat.com" , "dev.jain@arm.com" , "yuzenghui@huawei.com" , "gor@linux.ibm.com" , "jackabt@amazon.co.uk" , "daniel@iogearbox.net" , "agordeev@linux.ibm.com" , "andrii@kernel.org" , "mingo@redhat.com" , "aou@eecs.berkeley.edu" , "joey.gouly@arm.com" , "derekmn@amazon.com" , "xmarcalx@amazon.co.uk" , "kpsingh@kernel.org" , "sdf@fomichev.me" , "jackmanb@google.com" , "bp@alien8.de" , "corbet@lwn.net" , "ackerleytng@google.com" , "jannh@google.com" , "john.fastabend@gmail.com" , "kas@kernel.org" , "will@kernel.org" , "seanjc@google.com" References: <20260114134510.1835-1-kalyazin@amazon.com> <20260114134510.1835-8-kalyazin@amazon.com> <294bca75-2f3e-46db-bb24-7c471a779cc1@amazon.com> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; keydata= xjMEY+ZIvRYJKwYBBAHaRw8BAQdA9FwYskD/5BFmiiTgktstviS9svHeszG2JfIkUqjxf+/N JU5pa2l0YSBLYWx5YXppbiA8a2FseWF6aW5AYW1hem9uLmNvbT7CjwQTFggANxYhBGhhGDEy BjLQwD9FsK+SyiCpmmTzBQJnrNfABQkFps9DAhsDBAsJCAcFFQgJCgsFFgIDAQAACgkQr5LK IKmaZPOpfgD/exazh4C2Z8fNEz54YLJ6tuFEgQrVQPX6nQ/PfQi2+dwBAMGTpZcj9Z9NvSe1 CmmKYnYjhzGxzjBs8itSUvWIcMsFzjgEY+ZIvRIKKwYBBAGXVQEFAQEHQCqd7/nb2tb36vZt ubg1iBLCSDctMlKHsQTp7wCnEc4RAwEIB8J+BBgWCAAmFiEEaGEYMTIGMtDAP0Wwr5LKIKma ZPMFAmes18AFCQWmz0MCGwwACgkQr5LKIKmaZPNTlQEA+q+rGFn7273rOAg+rxPty0M8lJbT i2kGo8RmPPLu650A/1kWgz1AnenQUYzTAFnZrKSsXAw5WoHaDLBz9kiO5pAK In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.106.82.9] X-ClientProxiedBy: EX19D004EUC001.ant.amazon.com (10.252.51.190) To EX19D005EUB003.ant.amazon.com (10.252.51.31) X-Stat-Signature: 7srqetiams6x8e6fuhr6jhoe9bf4ga9e X-Rspam-User: X-Rspamd-Queue-Id: C314B1C0011 X-Rspamd-Server: rspam08 X-HE-Tag: 1768584511-211988 X-HE-Meta: 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 EA4sWncz 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 GZd3SajG Axz9uKuGzJOrhcbDjQ0GgBVYrXCOxsEYkXNNGCdipyQ= 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: List-Subscribe: List-Unsubscribe: On 16/01/2026 15:34, Edgecombe, Rick P wrote: > On Fri, 2026-01-16 at 15:00 +0000, Nikita Kalyazin wrote: >>> Does this assume the folio would not have been split after it was >>> zapped? As in, if it was zapped at 2MB granularity (no 4KB direct >>> map split required) but then restored at 4KB (split required)? Or >>> it gets merged somehow before this? >> >> AFAIK it can't be zapped at 2MB granularity as the zapping code will >> inevitably cause splitting because guest_memfd faults occur at the >> base page granularity as of now. > > Ah, right since there are no huge pages currently. Then the huge page > series will need to keep this in mind and figure out some solution. > Probably worth a comment on that assumption to help anyone that changes > it. Makes sense. I'll leave a comment. > > I imagine this feature is really targeted towards machines running a > bunch of untrusted VMs, so cloud hypervisors really. In that case the > direct map will probably be carved up pretty quick. Did you consider > just breaking the full direct map to 4k at the start when it's in use? That's an interesting point, I haven't thought about it from this perspective. We should run some tests internally to see if it'd help. This will likely change with support for huge pages coming in though.