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 89C9BD11183 for ; Thu, 27 Nov 2025 11:18:25 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B30726B0012; Thu, 27 Nov 2025 06:18:24 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B07F66B0022; Thu, 27 Nov 2025 06:18:24 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A44CC6B002A; Thu, 27 Nov 2025 06:18:24 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 92C6F6B0012 for ; Thu, 27 Nov 2025 06:18:24 -0500 (EST) Received: from smtpin30.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 24C9813BF57 for ; Thu, 27 Nov 2025 11:18:24 +0000 (UTC) X-FDA: 84156138528.30.5DB5B21 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf04.hostedemail.com (Postfix) with ESMTP id 92B5240003 for ; Thu, 27 Nov 2025 11:18:22 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=HnqFtZWD; spf=pass (imf04.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1764242302; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=knHI4LCoYOCm7lwQ3FWEiwAFh6Y9pjycr2PvFvs1X4w=; b=Z8+lvqNxe0L2FLrRr8Y/A3KL6XRJmVFWrrZLJnMHJdvZO97ii388cBTmwS0QYvquP79lQ4 fVQAZpXRDWRimW5wfD4DYA2347AFxxdqr/qL16x1kHLdRQ9bYUx3/haCwuqP+iEJ4puPIV o1+Aq66QIIxv7/YfQ/qMEJCAYp4WXTE= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=HnqFtZWD; spf=pass (imf04.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1764242302; a=rsa-sha256; cv=none; b=isHleORHpQUEOFSJ6Lhri0dYTHvr8hAIj6IY+LqHgOZjdNeUI1hx0U7VysIVNgCROZ37Kf tKl7n5SxebkTsaq2UlB9BIp/AmgYx8Xl1PeTVh7X1473iEp5nryoTmyeF4ufjOZEFUGsSV vj994rcn7aV53kFk74fzg+kT2QaGSr4= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 0A09C60204; Thu, 27 Nov 2025 11:18:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7BAA0C4CEF8; Thu, 27 Nov 2025 11:18:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1764242301; bh=LGIVtxajxKFoRcUUjJf+GTVcZh6OJXHRfbkkB9FrCW4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HnqFtZWDotDk1h+8DKJczwnhvfeDRKlb5rj1/zSdBmYiKSz8nz78NxKpSyPtHeUdu 4n8L4Zd2gwlN/B7LPcFoZyS/zWBZXIv9OMpMIFYn71ZaER/U5xSNynksfK0sM/XxgB YgehyVIJixQt0yYyutGkCdsw9Zd17a00okzKK4aj7IPBjRy0905NjNYpwyleZGqwYa M4Dbkn+DHnFDyZ1VC9l2lWarWa6HrCoitN/w/rxXyKDjrYuxWaWBrZGdly1ctiDQMR xF8qUP8fHzba9Df2M7ahFMZ3bMHUXoIpUZpDd3OPmk2ndqD0XUMvJBopJIapbLfyIE BeUlxurO7d9Rw== Date: Thu, 27 Nov 2025 13:18:10 +0200 From: Mike Rapoport To: Peter Xu Cc: linux-mm@kvack.org, Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Nikita Kalyazin , Paolo Bonzini , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, "David Hildenbrand (Red Hat)" Subject: Re: [PATCH v2 3/5] mm: introduce VM_FAULT_UFFD_MINOR fault reason Message-ID: References: <20251125183840.2368510-1-rppt@kernel.org> <20251125183840.2368510-4-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: sf4mt37ax3gnutsohpi9k87bxn7c5go8 X-Rspam-User: X-Rspamd-Queue-Id: 92B5240003 X-Rspamd-Server: rspam09 X-HE-Tag: 1764242302-317900 X-HE-Meta: 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 Eea2onZH FEuSbYkaHwzoEK6VURTeItnkJyp8oHwGf/p1dW6X8PNXiZyaNp1UIXcZ0lyN2Q0HJfYTdpAbCsz9wBsSR2Ql2Neyt44nzV5zqjPY3lrQ1QO+y8afEYIsPm9I427mTkLDn3Ppv98eY1EIPWt0ZulkZzCRQFmKO7l2eXXp6q/C9Gl9577zHmiEDNxJaHkmQHmoZ6EPtw2HNTDpilDNOBXAI5eDkJ59OUB71MXeVVczdxQ/ZXAjSCTQk07u3KaENus5S3Yrq9ik7mXu4cwYQdUatoSsDeej9/OnfHeFyaIjLqEegU6amM16uyOoysFpC7iw9m/udiBQPnUAIWU0= 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 Tue, Nov 25, 2025 at 02:21:16PM -0500, Peter Xu wrote: > Hi, Mike, > > On Tue, Nov 25, 2025 at 08:38:38PM +0200, Mike Rapoport wrote: > > From: "Mike Rapoport (Microsoft)" > > > > When a VMA is registered with userfaulfd in minor mode, its ->fault() > > method should check if a folio exists in the page cache and if yes > > ->fault() should call handle_userfault(VM_UFFD_MISSING). > > s/MISSING/MINOR/ Thanks, fixed. > > new VM_FAULT_UFFD_MINOR there instead. > > Personally I'd keep the fault path as simple as possible, because that's > the more frequently used path (rather than when userfaultfd is armed). I > also see it slightly a pity that even with flags introduced, it only solves > the MINOR problem, not MISSING. With David's suggestion the likely path remains unchanged. As for MISSING, let's take it baby steps. We have enough space in vm_fault_reason for UFFD_MISSING if we'd want to pull handle_userfault() from shmem and hugetlb. > If it's me, I'd simply export handle_userfault().. I confess I still don't > know why exporting it is a problem, but maybe I missed something. It's not only about export, it's also about not requiring ->fault() methods for pte-mapped memory call handle_userfault(). > Only my two cents. Feel free to go with whatever way you prefer. > > Thanks, > > -- > Peter Xu > -- Sincerely yours, Mike.