From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E2D6F472F95; Thu, 10 Sep 2026 11:32:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789039937; cv=none; b=s0aPGqTonIWHkvqtdlgIvLEUMcPfO1RZyVZul32Y3lJJ3TccvzE6SRVUD3tcocWcCKOzWdOEg2ZjvM0NSAxD4Cfkg2NZABZO/Y7dhpZg56+Vwjwbf2vYJbMYx1UTcYv9UWhq8pgiWYPmrByd+6ManBAH8ilQyborWPaIn9vQYXU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789039937; c=relaxed/simple; bh=EuV5QIX2mAp12NIU28Nd25M4uUJSmYTi7bD3oeSAC3A=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=qGZYV8+Ynfo6zIWGIb09KWqs6ZW1Gb5DqbDD5F0WwIjS9/ebUM26Hf6BSWrx0wFHls9msdnW5NS6TS5bG6XB29HRyiwVJ040NuCqdaTYZCqm92vu4K0PvBST1OBxPWsdRTja1zpjc6ORlAGgHqc+7g+56DNI2etH1qvjvUiP/xM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Nq7aTfP6; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Nq7aTfP6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E33991F000FF; Thu, 10 Sep 2026 11:32:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; 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 Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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