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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789048823; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=en3cnLSz3rou/qEMJvX8ynI+F/sbMoUWhXxA8YlL6Ro=; b=pF22G78IUle9dnuD4FGP9uN3SbrAEs0Iq9+cgjPLBihxwbkGwXkuwDabSPAOpqKXWCRy28 OcSluSTzEguoVrmgIvUDcK8Gt+IqF4WKUh4HoVPgd6WTN1NvI+Oxafb4R9pHjqxF9NIc00 z+8r4silmqLQ4kNAdMFUSG5iwTFA8Sc= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 55F84600CB; Thu, 10 Sep 2026 14:00:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5FC131F000FF; Thu, 10 Sep 2026 14:00:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789048822; bh=en3cnLSz3rou/qEMJvX8ynI+F/sbMoUWhXxA8YlL6Ro=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=blwkdE5QaCyKLuWw769dVAe7GqgyZGrHD9jp61Y7efv6M8KCj8uE12v4fDkaUrPMY HvQzf0ChhszWc5zTCCOihSbPLfFivsmBe4jmZ0EqbUnvmOgjqugMRsoXSECB4SD3qO /BXgi69/v2LxgFq6yYk8MlrrJnzW10TrVlGIc+HmH1k8viT8RdpEMwMtWz0OknlCES vDY1+zDfG7X9NZHoRWvjpd50yrPjlDNT2BSSdLRL/OlVYYlqxP5SFSEDdHxoG/xFQS bzfwkcR80B7EcfF8xQIZJCGvVS4IsyDj9SLCmaSXBNG6OxAcEwXKd6pbqh7WEb1d2/ iCZ1b4nRh/aEQ== Message-ID: <580e45c7-7f4e-4fbd-b73d-3bbd048fbc6b@kernel.org> Date: Thu, 10 Sep 2026 16:00:13 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/5] KVM: guest_memfd: bind backing memory to a NUMA node To: Gregory Price Cc: Ackerley Tng , linux-mm@kvack.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, pbonzini@redhat.com, seanjc@google.com, akpm@linux-foundation.org, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, shuah@kernel.org References: <20260902194657.79075-1-gourry@gourry.net> <0386eb30-0e0c-4d8c-abfe-86161b9e3d1f@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 01663A0005 X-Stat-Signature: xkqc1rzbirecwdstyjrgbkz65815mej1 X-HE-Tag: 1789048822-608265 X-HE-Meta: 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 8oxijxcO zv6x29+GVersxsN6HnKXw+WriTA9S17+QdWPoa9IUgWUpKFB6/k2WT196CjjapcBDsqwq/45h+b9iQ3JareN4PjIbgUyU44X/2OAoRU6JDisK+uiWYLAZ9fDvOTxAc3YoeDksIIGg7Dmn6HWpi3GXGlJVmYzgpRtapLpAje2qepw7fdKOt+9jqrppPsTGDTGmv0EVT/vURk9+gfx4cGy+3jAfLIMQRLubcr/ElhAgj/YHHe1UdafysCt3CNcO9RVv8/JGSiSBV7GAMQpnMDUSZxc5e+pVHyGwWll8b3K2SAr5Cl9XRRTU7lNUDglqOzdXPjUzYc6kIB5kWlsnDAJG59r8P7x+GNUj4BgRr1KVQC6NyYeVghKQHAOkhtcFECiUAFsh Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/10/26 15:39, Gregory Price wrote: > On Thu, Sep 10, 2026 at 01:32:08PM +0200, David Hildenbrand (Arm) wrote: >>> >>> the eventual intent is to enable this for fully confidential, >>> host-unmapped guest, isolated to a particular memory device. >>> >>> Requiring a mapping to get node-placement is quite defeating the point. >> >> You only need a VMA, not actually mapped/faulted pages. So I don't immediately >> see the problem? >> > > There is no VMA here - only an inode (GMEM_I), which is where the > shared policy hangs off of. > > So yeah, if there was a vma, that's i suppose the missing component > needed to hook up userland mempolicy to all of this - but I would have > thought creating a VMA for guest_memfd is hacky and confusing (since its > intent is to basically not have a VMA). The VMA is irrelevant, you just don't want to fault in the pages. In fact, you'd only need the VMA while setting the policy. (similar to shmem) > > Is there a series I missed that was proposing this? I recall that we definitely discussed this in on of our meetings, but I don't remember whether we decided to not fully support this case given that in-place conversation is on the horizon. I think you can open a private-only guest_memfd with GUEST_MEMFD_FLAG_MMAP, and it will reject to fault-in any pages, but GUEST_MEMFD_FLAG_MMAP also changes the way memory pages are obtained: "When the KVM MMU performs a PFN lookup to service a guest fault and the backing guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always be consumed from guest_memfd, regardless of whether it is a shared or a private fault". For shared-only that makes perfect sense. For private-only, where shared memory pages would come from a user VMA, this wouldn't really work. But I don't know how your case would look like (where are shared pages? are there any ever?) -- Cheers, David