From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0573D7F; Fri, 23 Feb 2024 00:35:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708648533; cv=none; b=BaGMQK2GT19P3OBGKFDEQv0zeQ2srRiroCn5pv4Z0WituptNg7f/9wXIROOHuwSv+bWs/dOvkuoUvN1skqM6Gqp1GEMxsqVbEJ7bu1Oyv3PzabsGEGsaGO3BZrjFpnp5d6J7Yi+95grfy52aN8CPMwvhmq9JwmPL1wj7DG5nNUo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708648533; c=relaxed/simple; bh=UuyemN29n5uuhM3XDRw+M9OmUMLgiLVssyaJZggKbgk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XogQ7iGgEmd0nDSXjAqYTLftPahvBtlMTvWgEIT+idEm7GOM8Ah04mamgMF/GjN8zZz6KOXDT82l0i4ZNqHKyGwet3+Xx/veaPynMSFfCdljfeanjjwzMkjBA79dwRT8DCsh32R/JBw5HKnvAsU70DMVCdNJi4cFa8IxkUR9gNc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=vx0lAI9O; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="vx0lAI9O" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Jjp0B9J5MnbOQoNMfaQog5UT9Wod0mD1lECH/WlLFiA=; b=vx0lAI9OP3zaj26NbO7YK2kxuL rxq6qOocccU9w2yUa/5HMJoRpmtWfr+tBtPwB+CGJECRTiFCjdwO5xc5UdSmb972zkdu7BjD+uqC5 ubiywajEuHOhv+hTCpDNgKXvOFPOegHcx3eRaKYh0dYMiRr3sKWWbb8Tcxj/kjKgeZAVrAS37kNCX 4XJgXKFYPlIOre4tzu+X3ZDzObpdTyMo+OiTSRoAwIFiQuempCYRJ0SD+navq/qnVcArmH06rzeed 1K6vfCbFRmKdh5tUX6xlnrSqGHaBX5Y4ZjeoAnodqK5ny8r16TpruMlihybbAJDlbb6QhIETbTUAl /tcoXSJg==; Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rdJX5-00000005CET-0p6c; Fri, 23 Feb 2024 00:35:19 +0000 Date: Fri, 23 Feb 2024 00:35:19 +0000 From: Matthew Wilcox To: Fuad Tabba , kvm@vger.kernel.org, kvmarm@lists.linux.dev, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, yu.c.zhang@linux.intel.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com Cc: linux-mm@kvack.org Subject: folio_mmapped Message-ID: References: <20240222161047.402609-1-tabba@google.com> <20240222141602976-0800.eberman@hu-eberman-lv.qualcomm.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240222141602976-0800.eberman@hu-eberman-lv.qualcomm.com> On Thu, Feb 22, 2024 at 03:43:56PM -0800, Elliot Berman wrote: > > This creates the situation where access to successfully mmap()'d > > memory might SIGBUS at page fault. There is precedence for > > similar behavior in the kernel I believe, with MADV_HWPOISON and > > the hugetlbfs cgroups controller, which could SIGBUS at page > > fault time depending on the accounting limit. > > I added a test: folio_mmapped() [1] which checks if there's a vma > covering the corresponding offset into the guest_memfd. I use this > test before trying to make page private to guest and I've been able to > ensure that userspace can't even mmap() private guest memory. If I try > to make memory private, I can test that it's not mmapped and not allow > memory to become private. In my testing so far, this is enough to > prevent SIGBUS from happening. > > This test probably should be moved outside Gunyah specific code, and was > looking for maintainer to suggest the right home for it :) > > [1]: https://lore.kernel.org/all/20240222-gunyah-v17-20-1e9da6763d38@quicinc.com/ You, um, might have wanted to send an email to linux-mm, not bury it in the middle of a series of 35 patches? So this isn't folio_mapped() because you're interested if anyone _could_ fault this page, not whether the folio is currently present in anyone's page tables. It's like walk_page_mapping() but with a trivial mm_walk_ops; not sure it's worth the effort to use walk_page_mapping(), but I would defer to David.