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 DCD0DCFC269 for ; Fri, 21 Nov 2025 11:59:20 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0C1C36B00A0; Fri, 21 Nov 2025 06:59:20 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 099DC6B00A3; Fri, 21 Nov 2025 06:59:20 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F184C6B00A4; Fri, 21 Nov 2025 06:59:19 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id DF4386B00A0 for ; Fri, 21 Nov 2025 06:59:19 -0500 (EST) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id BBB1C140553 for ; Fri, 21 Nov 2025 11:59:18 +0000 (UTC) X-FDA: 84134468796.16.6AC10ED Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf16.hostedemail.com (Postfix) with ESMTP id 114A9180008 for ; Fri, 21 Nov 2025 11:59:16 +0000 (UTC) Authentication-Results: imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=C9rHWLou; spf=pass (imf16.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 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=1763726357; 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=/VC0rLK7avPdZ1/pOnGKaCiL3bqlIpNaltx3xnsyzdo=; b=UpdCrHKCPC88x1TjXzndFD8RZo9NjP4E7l+j/SoHLrLERTRJa5eglYY9dfeqbW4KczW8i0 Krrc3e7XtxzKAkGL/TMBJ9Bb6vC/cRMMQ9E56bWtl5U9Ey44lnU3+XNaipuNoNEioSMglX gE8ohq9PyGDzX1swvWUUqyLTiQuD43E= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=C9rHWLou; spf=pass (imf16.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 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=1763726357; a=rsa-sha256; cv=none; b=F0iUed2UkeSpRhnJYeiR4RPvaEQDbe/Fd7oBvZB1XxgNHseqEW9mHHD6/syzI8xCL0dNlp 3YgK2oxxVa0JsmypTlozv3mpIm63rdBhchuqxlmD4/WXjxHl9IUqDzTlXv/rC6oqbLKj04 99J0ERMQFfIX2+kNORCWaItCpGNzbEc= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id D0AB8434DC; Fri, 21 Nov 2025 11:59:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9B4F2C4CEF1; Fri, 21 Nov 2025 11:59:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763726355; bh=RiQAcjp2e+731JZhVL1+P6ye9ciRcuL6VvATes7vC24=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=C9rHWLou00pxAF6NJa4RQBnLlmDOL5cqA0B2wM2fNW2Yo3T5CM9n6+r1ARo/vkyv2 1tbDSVQCW4tGNdOwt/5PZe2wvr/qMDXRSCf4ncesFymiHBjirobG0VQ0xY33Yyg/kI spHo1UL+T48z36hpT02GI9B7/FVKFQkfgGu+0IxyHZoFAiojYLf7aEEair0maBs0oW 7g8PFSncyT4fKsVC/KlKZ/f6Ma5vzE7LZT4guENhM09Eda7055CiewP3iG9GVpUY2k fLjljE/8XCA+DyPPDQ4Js4IL0wa/hldO2IgPo6RPAb2j+csxcCPauHd3cA7DR1R3+3 7jFaYIvzEubMg== Date: Fri, 21 Nov 2025 13:59:05 +0200 From: Mike Rapoport To: "David Hildenbrand (Red Hat)" Cc: linux-mm@kvack.org, Andrea Arcangeli , Andrew Morton , Baolin Wang , Hugh Dickins , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Nikita Kalyazin , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [RFC PATCH 3/4] userfaultfd, guest_memfd: support userfault minor mode in guest_memfd Message-ID: References: <20251117114631.2029447-1-rppt@kernel.org> <20251117114631.2029447-4-rppt@kernel.org> <007c08e4-ce70-4c30-b3b1-e25e02dfe29d@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <007c08e4-ce70-4c30-b3b1-e25e02dfe29d@kernel.org> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 114A9180008 X-Stat-Signature: u3akush58qjkhqugys18irmw4xfjob34 X-Rspam-User: X-HE-Tag: 1763726356-482929 X-HE-Meta: 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 9YQrfkV0 xQ7CmKkUlL2gKnKcMOZL8rxPwLCaTaSQaMIvPRlRCnar0lIkL5nGCd2xcBzF/vyuIXeA5x7qsLo7KwaB/TlCSR94zS2UrrkDQm1EjX9g8XKpiZFmfMSQDGwfoSUiltAupjgmqTx11FAZxAvwpc9cWprZRUxM0HbLtmG3KUzBhrm/F5Rv4Ot4ol48uIBmre1GvSg0RY7mI4V4b1YDUlGSH24TIhkPGTOEhBCXUgsnj6ADtk5JtjB6TlFDYq2NroJsz9L6UI2JJGeckIYDP5Z/PWpJgQzIp+s8+YVbvmSGxBR79GTI= 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 18, 2025 at 05:41:13PM +0100, David Hildenbrand (Red Hat) wrote: > On 17.11.25 12:46, Mike Rapoport wrote: > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > > index fbca8c0972da..5e3c63307fdf 100644 > > --- a/virt/kvm/guest_memfd.c > > +++ b/virt/kvm/guest_memfd.c > > @@ -4,6 +4,7 @@ > > #include > > #include > > #include > > +#include > > #include "kvm_mm.h" > > @@ -369,6 +370,12 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) > > return vmf_error(err); > > } > > + if (userfaultfd_minor(vmf->vma)) { > > + folio_unlock(folio); > > + folio_put(folio); > > + return handle_userfault(vmf, VM_UFFD_MINOR); > > + } > > Staring at things like VM_FAULT_NEEDDSYNC, I'm wondering whether we could have a > new return value from ->fault that would indicate that > handle_userfault(vmf, VM_UFFD_MINOR) should be called. > > Maybe some VM_FAULT_UFFD_MINOR or simply VM_FAULT_USERFAULTFD and we > can just derive that it is VM_UFFD_MINOR. _UFFD_MINOR sounds better, maybe we'll want something for missing later on. > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 4f66a3206a63c..2cf17da880f0e 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -1601,6 +1601,8 @@ typedef __bitwise unsigned int vm_fault_t; > * fsync() to complete (for synchronous page faults > * in DAX) > * @VM_FAULT_COMPLETED: ->fault completed, meanwhile mmap lock released > + * @VM_FAULT_USERFAULTFD: ->fault did not modify page tables and needs > + * handle_userfault() to complete > * @VM_FAULT_HINDEX_MASK: mask HINDEX value > * > */ > @@ -1618,6 +1620,7 @@ enum vm_fault_reason { > VM_FAULT_DONE_COW = (__force vm_fault_t)0x001000, > VM_FAULT_NEEDDSYNC = (__force vm_fault_t)0x002000, > VM_FAULT_COMPLETED = (__force vm_fault_t)0x004000, > + VM_FAULT_USERFAULTFD = (__force vm_fault_t)0x006000, > VM_FAULT_HINDEX_MASK = (__force vm_fault_t)0x0f0000, > }; > @@ -1642,6 +1645,7 @@ enum vm_fault_reason { > { VM_FAULT_FALLBACK, "FALLBACK" }, \ > { VM_FAULT_DONE_COW, "DONE_COW" }, \ > { VM_FAULT_NEEDDSYNC, "NEEDDSYNC" }, \ > + { VM_FAULT_USERFAULTFD, "USERFAULTFD" },\ > { VM_FAULT_COMPLETED, "COMPLETED" } > struct vm_special_mapping { > > > IIUC, we have exactly two invocations of ->fault(vmf) in memory.c where > we would have to handle it IIUC. And the return value would never leave > the core. I've found only one :/ But nevertheless, I like the idea to return VM_FAULT_UFFD_MINOR from ->fault() and then call handle_userfault() from __do_fault(). > That way, we wouldn't have to export handle_userfault(). > > Just a thought ... > > -- > Cheers > > David -- Sincerely yours, Mike.