From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4439749B21B for ; Tue, 1 Sep 2026 18:26:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788287209; cv=none; b=VfKC7RsHly8pDiJIDCPzql0UJnWEYfpFxCy1+38SA92naa6igGKLMGKpjqnpOgWeqKcyX8J3glkWv1eNP+EqVjTHhQ4OLnhqQyXY1F5+5mawcdh9kQpDhJvhPGnELEdB9vlReugd9wwabgxVSjoDkEul3qOVZj93vh1AH0qsfc8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788287209; c=relaxed/simple; bh=vz7vfk19Z+bqyE6zKwD5krwa/0p2VNqmkC4gZJtUZS4=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=izyMS2fkKCwT3HCDHaTx7R1E7AoqBYEQ/HLxtLQQUd0Rxy5x5PsPMZu62cVazTXTxHsdWObtuZIUWUowwShsIIplIdZMRRh2W2gMPrQuSdocewGsFeF5TdrNQ42AON7aJ0vq21dgD6XsW5gJERiKrec6qUUdmsY7yItgXfHXcaM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=nxB8465w; arc=none smtp.client-ip=209.85.215.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="nxB8465w" Received: by mail-pg1-f199.google.com with SMTP id 41be03b00d2f7-cbb20f82a0eso144419a12.0 for ; Tue, 01 Sep 2026 11:26:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1788287207; x=1788892007; darn=vger.kernel.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=5v8dwO4qIccjpXs9ZdhBw1lluA5t2BNdQSYlylga9bQ=; b=nxB8465wd02jxyXSBEDLq4Idb0QJSWjaR0KxrjK2ITfpNGuKegdz1Pxa76jdytfIiw vYUIkwuZECZXAAw/H8tlVTN9/2hyvUIw7K4/dfIFKlWMzJj0OjpEfHayidTeqvIX1lik j686n8m+uMuii79vRA5CZ+1nW7KzMnQYulgg6tzwqzIOhGciNmX2N+CDq1xTc1SWbmYQ gh0doBDhGcEtYsePeLeaJtXCW17bN6xhNnW0ctQZlmikL9WyGNtiicLPFHmHRhoE38+5 YU2YIJ6IF0SgyeoerLjvTX7NZDrLYgsOdnaG8uVl7J/azPKP4e/UbC8p1qrCp++Umqz0 yuLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1788287207; x=1788892007; 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=5v8dwO4qIccjpXs9ZdhBw1lluA5t2BNdQSYlylga9bQ=; b=AeZzR+/Il8eosC7q0pR+Q1UX7XIPhZythPhO0pHhdavi7VnQ9m1xt6RQpZLc1DNYed jcBYWfzmyvr8CJiLdC1POcreAN8IvPiYipT/auXUuW+7aVcoimSgbn+BmatwUKCNoyVw /9qiiKQW/o1M+EJZo1Aepl5ea/7C4fSeaWUKiAOQSz3HxIyFA1Nvc7zVHp2yI9L1UKhd UOp+RZO5bUJy8Zs7J/uvQyiaT7oC0aKdoe8G6QV8n6voIv9VTBo4i1kzJBVOl+sou5wz ViO2027qOSoqAo4ho6WjBs6UDakmvdctLlLfkp/rNmOA3hv8uLxBSGk4GWbNlOJGh7Ie 73TQ== X-Forwarded-Encrypted: i=1; AHgh+RrTP7Kz9gXpl3zB4IlpnZzTPjqGi/BExNk9M04SAtF+hHT5QX9ypKQ1O9OFAlGoXUwJFTw=@vger.kernel.org X-Gm-Message-State: AFuF++mCt3uifu+ho+rpvywVE+C6Brk8zrrktC+SrN+rusRl/2Yqa98+ UUOHIRtiCNudr+7eWVxyJASXArCFx0UN55fIWOWaEhidSRqFpnkKAUtCLwgb96ZtZhbeQpZ16PY Tj8eW9g== X-Received: from pgbd18-n1.prod.google.com ([2002:a05:6a02:64d2:10b0:cc3:28ba:e8b1]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:7284:b0:3d0:cc29:ff63 with SMTP id adf61e73a8af0-3d7ae4ed97emr13763648637.12.1788287205983; Tue, 01 Sep 2026 11:26:45 -0700 (PDT) Date: Tue, 1 Sep 2026 11:26:45 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260830-gmem-inplace-conversion-v12-0-85e5fd25252a@google.com> <20260830-gmem-inplace-conversion-v12-23-85e5fd25252a@google.com> Message-ID: Subject: Re: [PATCH v12 23/45] KVM: Let userspace disable per-VM mem attributes, enable per-gmem attributes 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, Xiaoyao Li Content-Type: text/plain; charset="us-ascii" On Tue, Sep 01, 2026, Fuad Tabba wrote: > Hi Sean, Ackerley, > > On Mon, 31 Aug 2026 at 01:25, Ackerley Tng via B4 Relay > wrote: > ... > > + kvm.gmem_in_place_conversion= > > + [KVM] Controls whether KVM enables in-place conversion > > + support for guest_memfd and tracks the private/shared > > + state of memory per guest_memfd instead of per VM. > > + > > + If enabled, KVM enables the KVM_SET_MEMORY_ATTRIBUTES2 > > + ioctl on guest_memfd file descriptors and disables the > > + legacy VM-scoped KVM_SET_MEMORY_ATTRIBUTES ioctl for > > + private memory state tracking. Only the > > + KVM_MEMORY_ATTRIBUTE_PRIVATE attribute moves to > > + per-guest_memfd tracking; other attributes remain > > + per-VM. > > + > > + This parameter toggles KVM's in-place conversion > > + capability support. Whether a VMM uses separate backends > > + or out-of-place memory management is determined by > > + userspace VMM design. > > + > > + Note, this parameter is only available when > > + CONFIG_KVM_VM_MEMORY_ATTRIBUTES=y. When > > + CONFIG_KVM_VM_MEMORY_ATTRIBUTES is not set, in-place > > + conversion is unconditionally enabled. > > + > > + Default is Y (on). > > The parameter is only settable when CONFIG_KVM_VM_MEMORY_ATTRIBUTES=y, and > in that config gmem_in_place_conversion initialises to > !IS_ENABLED(CONFIG_KVM_VM_MEMORY_ATTRIBUTES), i.e. N, not Y. Is the doc line > wrong, or is N-by-default not what was intended here? The doc is wrong. The intent is to maintain backwards compatibility with existing deployments if KVM_VM_MEMORY_ATTRIBUTES=y. > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 05c518c9b8078..929fd3e1a01e6 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -103,7 +103,10 @@ static bool __ro_after_init allow_unsafe_mappings; > > module_param(allow_unsafe_mappings, bool, 0444); > > > > #ifdef kvm_arch_has_private_mem > > -bool __ro_after_init gmem_in_place_conversion = false; > > +bool __ro_after_init gmem_in_place_conversion = !IS_ENABLED(CONFIG_KVM_VM_MEMORY_ATTRIBUTES); > > +#ifdef CONFIG_KVM_VM_MEMORY_ATTRIBUTES > > +module_param(gmem_in_place_conversion, bool, 0444); > > +#endif > > EXPORT_SYMBOL_FOR_KVM_INTERNAL(gmem_in_place_conversion); > > #endif