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 9EF32C624D0 for ; Tue, 1 Sep 2026 18:35:21 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id A933D6B00A3; Tue, 1 Sep 2026 14:35:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A6A696B00A4; Tue, 1 Sep 2026 14:35:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 980386B00A5; Tue, 1 Sep 2026 14:35:20 -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 66C816B00A3 for ; Tue, 1 Sep 2026 14:35:20 -0400 (EDT) Received: from smtpin27.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id CE57540504 for ; Tue, 1 Sep 2026 18:35:19 +0000 (UTC) X-FDA: 85166045958.27.6052344 Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) by imf01.hostedemail.com (Postfix) with ESMTP id 23F004000B for ; Tue, 1 Sep 2026 18:35:17 +0000 (UTC) Authentication-Results: imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20251104 header.b=SyiYakrz; spf=pass (imf01.hostedemail.com: domain of 35BqXagYKCNEF1xA6z3BB381.zB985AHK-997Ixz7.BE3@flex--seanjc.bounces.google.com designates 209.85.215.200 as permitted sender) smtp.mailfrom=35BqXagYKCNEF1xA6z3BB381.zB985AHK-997Ixz7.BE3@flex--seanjc.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788287718; b=gBQRhqH8BNhWbQH5pFMBobW3d4uvaXPTMdIkcp9wRNfTR/MPsm9LVNpfNDyA+ZCkVPNq/A +f/FFDyzTTuKb0VArxHWrLI0NzwQ1hsApiXCetLY7M7zyBp+dIf0AXXkyCou744dBe55EI mpcMFQRhZuXQIchbMt8xK//RS8wdr0Q= ARC-Authentication-Results: i=1; imf01.hostedemail.com; dkim=pass header.d=google.com header.s=20251104 header.b=SyiYakrz; spf=pass (imf01.hostedemail.com: domain of 35BqXagYKCNEF1xA6z3BB381.zB985AHK-997Ixz7.BE3@flex--seanjc.bounces.google.com designates 209.85.215.200 as permitted sender) smtp.mailfrom=35BqXagYKCNEF1xA6z3BB381.zB985AHK-997Ixz7.BE3@flex--seanjc.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788287718; 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=LA0MtyhL9+n6pP8AlY+vz7qS2JveEW6zRalGa05+rBs=; b=XYgesaK8JvAC1B3e6ocp1cWX26pOqXxz1g6iBoRgo/SP+WPRZaHpRsx/w9QfQI8XHo55Kp iLuCTHXBSTWDg/cWmcgihKX3XC+OeRbiJykvmih/2lS2Ai3sCFflNKw+sK6LEL+zfS2upQ AKgy3fYbgm5LdDW7mQT5vAOHipKNvKE= Received: by mail-pg1-f200.google.com with SMTP id 41be03b00d2f7-cc1d85c012dso302588a12.2 for ; Tue, 01 Sep 2026 11:35:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1788287717; x=1788892517; darn=kvack.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=LA0MtyhL9+n6pP8AlY+vz7qS2JveEW6zRalGa05+rBs=; b=SyiYakrzgRBIXplQeIHc71lmAvDv28CjEdj5HZUsWQ1uu8tC+cO831RnpgsjDy6JL3 c7/fkpRSpSJMmh6mbQeNbizfJPVDdb7W48f6aubTA0hSp1/wh4mGcJ1kmGR9ppcI2CFQ T2o/kvNq1Kw01YRy/W5rJZt8NFC76xOZirErZFcOAojfQfbIrxQjJVRkpGEBk7Q6fxlz DqiNJq4ZmzRRoHYqYSizEm8ftrx/6BiVfeXNzMAj7rN4pIOANF2YLLCGZ1ufub6lfHIH 6PKxleFiqfpd0TXH3IBqzIAw3AIFrHn8eIarzMsMBZvAPmIEMWjxfEl3ir2B0d6AyFiP X8HA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1788287717; x=1788892517; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=LA0MtyhL9+n6pP8AlY+vz7qS2JveEW6zRalGa05+rBs=; b=DZ01Cw/36UCVKVPiihtvzmCjwkNQI/ml0e0ubSw1tFm8r8ciJXuE1UZts+sQh5cjyC +SpV7FAdDWkYSOJCTEO3wVul1QaEUK+w8X/lh1lglRTOEYd8LqGfq+/U1epHloYrqgBn yrx5x+N54HLu3qvdCQh1IKCy42dXGwCCLTXI8AK13/MIL8xeQ15sg4Oz5TuQDGlsgx6x lFAO40DZ+3Nm66a9D+RlykuXaNiLircQBD6rfPtgGaRKAdFiZD4YywVUrfS31Osd8P1F M2ULOBv0QKUdEvCA6r9GICVfM1knU5xo2EvoK8mM4LcHPOQNOcWUaxAVQLJUcjzOBefP DSdQ== X-Forwarded-Encrypted: i=1; AHgh+RrGW1inlH5GkcY/O1a5vktqA2+9e/cdWJDK63H1LWmx8OKlmFh+C4Go6fGVj5lQ8BJwNBAzhOPFTg==@kvack.org X-Gm-Message-State: AFuF++k2/nAsmMkec3edhiVdruRoZIG3kKj2s9Pt4llpfkZoH7cz6NU+ uihMfpUiG2YWfIMAp2maNp+8Z7FVmmL/dO6+Yeij5Xr0DH7lO9d6QiNWqxWbNQTum2Xb40Fydbc ZnWThGw== X-Received: from pgcv12.prod.google.com ([2002:a05:6a02:530c:b0:c96:acc6:54d6]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:3944:b0:3d3:aec2:4dcb with SMTP id adf61e73a8af0-3d7b075b26bmr19293744637.23.1788287716571; Tue, 01 Sep 2026 11:35:16 -0700 (PDT) Date: Tue, 1 Sep 2026 11:35:15 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260830-gmem-inplace-conversion-v12-0-85e5fd25252a@google.com> <20260830-gmem-inplace-conversion-v12-15-85e5fd25252a@google.com> Message-ID: Subject: Re: [PATCH v12 15/45] KVM: guest_memfd: Ensure pages are not in use before conversion From: Sean Christopherson To: Fuad Tabba Cc: ackerleytng@google.com, aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , tarunsahu@google.com, Randy Dunlap , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev Content-Type: text/plain; charset="us-ascii" X-Rspam-User: X-Stat-Signature: dhs5s9gqteo1cs7ew9b1tqpo5s6wtsrb X-Rspamd-Queue-Id: 23F004000B X-Rspamd-Server: rspam06 X-HE-Tag: 1788287717-131481 X-HE-Meta: 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 pWwxEhk9 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 01, 2026, Fuad Tabba wrote: > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > > index 803c7cdbbe0f6..fe02c47c85fb5 100644 > > --- a/virt/kvm/guest_memfd.c > > +++ b/virt/kvm/guest_memfd.c > > @@ -538,8 +538,46 @@ static int kvm_gmem_mas_preallocate(struct ma_state *mas, u64 attributes, > > return mas_preallocate(mas, xa_mk_value(attributes), GFP_KERNEL); > > } > > > > +static bool kvm_gmem_has_outstanding_references(struct inode *inode, > > + pgoff_t start, size_t nr_pages, > > + pgoff_t *err_index) > > +{ > > + struct address_space *mapping = inode->i_mapping; > > + pgoff_t last = start + nr_pages - 1; > > + bool has_outstanding = false; > > + struct folio_batch fbatch; > > + pgoff_t next; > > + int i; > > + > > + folio_batch_init(&fbatch); > > + > > + next = start; > > + while (has_outstanding && filemap_get_folios(mapping, &next, last, &fbatch)) { > > has_outstanding starts as false, so the loop never runs and the function > always returns false. The outstanding-reference check is dead at this > patch, so a to-private conversion would not be rejected even when a page > still has an outstanding reference. > > It's fixed later in "KVM: guest_memfd: Handle lru_add fbatch refcounts > during conversion safety check", which changes the condition to > !has_outstanding. I think that fix belongs in this patch, so the check > works when it is introduced and the series bisects cleanly. Why even bother with has_outstanding? Avoiding it requires copy+pasting folio_batch_release(), but it's less code and IMO the end result is a lot easier to follow: struct address_space *mapping = inode->i_mapping; pgoff_t last = start + nr_pages - 1; struct folio_batch fbatch; pgoff_t next; int i; folio_batch_init(&fbatch); next = start; while (filemap_get_folios(mapping, &next, last, &fbatch)) { for (i = 0; i < folio_batch_count(&fbatch); ++i) { struct folio *folio = fbatch.folios[i]; /* * Outstanding references are anything other than those * from the page cache, plus 1 temporary reference held * by filemap_get_folios() in the folio batch. */ if (folio_ref_count(folio) != folio_nr_pages(folio) + 1) { *err_index = max(start, folio->index); folio_batch_release(&fbatch); return true; } } folio_batch_release(&fbatch); cond_resched(); } return false; and then we end up with: enum lru_cache_drained drained = LRU_CACHE_NOT_DRAINED; struct address_space *mapping = inode->i_mapping; pgoff_t last = start + nr_pages - 1; struct folio_batch fbatch; pgoff_t next; int i; folio_batch_init(&fbatch); next = start; while (filemap_get_folios(mapping, &next, last, &fbatch)) { for (i = 0; i < folio_batch_count(&fbatch); ++i) { struct folio *folio = fbatch.folios[i]; if (__folio_has_outstanding_references(folio, &drained)) { *err_index = max(start, folio->index); folio_batch_release(&fbatch); return true; } } folio_batch_release(&fbatch); cond_resched(); } return false;