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t=1789039935; bh=MUiE/SGANYmf8vtQog79LZ93gRF429+dekDwpOi8Koc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Nq7aTfP6tBPV9eSggpwSR/rrMKqYSL6MC2Z55EKE55t+xwqBzKxM+9gvpQOk9S6Rn PsEJX1wndnKviOpfAS40eS5HlNnlT6iJ/JAbhrIhI+AD84w56r+H/lYTbkA3Fl7XKw 8RGFi0sFpZRaS7kZmDvkHwUaUWVv6HWG3sJk818BFz7rS4FaxfYxxrRw8MfR3Yeblh fpG6G3GmBWTCdsMFoyZOEwxDie2RarDYhFh4UoAMuNYNXM8uBVRCe37/oMsd9nt7Mm 5f8e8jnPCKVe48CxyKMQAKZ1NxijCLSf2n5zKgf2BWeX+PDo7Nnt/D1VMAVjWG082V vOOStZGsLB16g== Message-ID: <0386eb30-0e0c-4d8c-abfe-86161b9e3d1f@kernel.org> Date: Thu, 10 Sep 2026 13:32:08 +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 , Ackerley Tng Cc: 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> 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: rspam08 X-Rspamd-Queue-Id: 5454B80003 X-Stat-Signature: qi8xsdnndxphb8xi96348y146g953y5y X-HE-Tag: 1789039936-248016 X-HE-Meta: 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 U8vF+BmI tVBsp3T8dAbcu4mT5eERvJAgj9EjTvxI955OevJQuaTJUddo0WSLmnSEwEimyA4JNEM5ZLobxaJMY27IgWyYDYHPuTlGy+kkj7WzZYlgzc1xTSmNqYId7hn3qANGp6BPkIW12wPgQiiBq0YUbOmbx8uQX1/ppojLLL6xtUjnasePbStXym8wFIAjjof+GGQmH6cp4MuP/mYec5JySe8Cdr5QtavmLCMrCdcjCWKfh5l5LVR+p3Sn1vNitYNaRIcUFT+ZcXq4Gb//+Irb2cZ1Fg3jdXB7LJsK7uoOZA69F1X2/R91HRYAwxjo1s5SnECV4QdZn2OdlIcefpi3qcFT+aE19N0prG0ssdmiJ4+xj+29QnYGm4C2BqeIAHGsPHZVgEPGjMtjXP3GyXCGj+mtCRM2k80pv4ItZfjO4jvQIEo0+IwL8lV5cPLPqaA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/10/26 01:10, Gregory Price wrote: > On Wed, Sep 09, 2026 at 03:41:35PM -0700, Ackerley Tng wrote: >> Gregory Price writes: >> >>> guest_memfd allocates its folios through a per-inode shared mempolicy. >>> >>> Today that policy can only be set after the fact, with mbind() on a host >>> mmap of the fd. That requires the fd to be mappable, and it cannot reach >>> folios that are only ever guest-faulted. Neither holds for a >>> non-mappable (confidential) guest_memfd. >>> >>> Add GUEST_MEMFD_FLAG_BIND_NODE and a node field to struct >>> kvm_create_guest_memfd. When set, KVM builds an MPOL_BIND policy for the >>> requested node and installs it over the whole inode, so every folio is >>> allocated there with no userspace mbind(). >>> >> >> Instead of a custom API to ensure all guest_memfd allocations come from >> a single node, how about these options? >> >> 1. Using cgroups/cpuset to constrain allocations (could be troublesome >> if the guest memory is not preallocated, unless the vCPU threads are >> running with the cpuset config) >> >> 2. Process-level NUMA policy >> > > for 1 and 2: > > the intent is to put the guest memory on the target node, not all system > memory for a given process. so the scope here is not the same. > > in fact at that granularity, the desired node may not even have eligible > memory to host the task's memory. > >> 3. Why not request the guest_memfd to be mmap-able just to be able to >> set a memory policy? >> > > 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? -- Cheers, David