From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.14]) (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 A91D240BCCE; Wed, 1 Jul 2026 11:07:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.14 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782904070; cv=none; b=iAiCYDOwdMC5Fk8lvbbDtVzSIV843u61DFo5MU77MF+OFGnaIbGVBUFvbrmQBkQYFtoSAKpii1qkYCRBjuXpQjqgohTdjDiMlODhcAptRsnKh4uy6jmQp4iXoIf5wKEPoAcWuOFQOgtidp+5V90yfUyxLLK98vpTo0wDV9kJhRk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782904070; c=relaxed/simple; bh=hCvnNk/pEx9Q3BuA3GT3urPlvNsb9ZGbJEO+TxrHDhk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ISrNKXq/pgcspmDOaD6vqghancW5wO0j1g1oXIIcH7YQ7L6uw0liZdMNqwM/8jb+ys7O1IL+d1alxdidV6SBxUwBgeJAFTfi+7XXNdcU58nWX3UFtu4OlG+Tu8Ky/okdRC3R+mvLVlNw85S1s1sUG+4KOtZwKW2R/uEFm8KVhbs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=LNtiPidL; arc=none smtp.client-ip=198.175.65.14 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="LNtiPidL" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1782904069; x=1814440069; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=hCvnNk/pEx9Q3BuA3GT3urPlvNsb9ZGbJEO+TxrHDhk=; b=LNtiPidLDPr2cCEfm6nmkpfeRNI4QV3/W9S1PF5JTllnEv0I5stLmP7R qJuecNfxVWxxeXE1ZFI90KMcIRSlQa2fjEy+w3ivHinUaseH7HJYePVui YMP73yvTHQM8rC+OltN8X/9K5IctoVX+GfNQFQi/Aa0Ib0PIFcGVluWQZ fs3D5IUYSOR+IoI313VcgY4t4gi/6mrajCQ33iaotHUCevuI03XwGAUs8 iXhqpbLpaR7r6hCZIdOhv9n2w1m/MV0nytJ+yUQykx+VtdMs5KWiGNLoR /bEUEmcL4nrfExvkAcvK50aiXyP87Y2TJO1Fl2xhVQYMZJTtOPxRBC6oo w==; X-CSE-ConnectionGUID: hFZnprObTNePX2nhndIJYw== X-CSE-MsgGUID: SfODCpYrQSa2FJ7OeXRYNg== X-IronPort-AV: E=McAfee;i="6800,10657,11833"; a="87546077" X-IronPort-AV: E=Sophos;i="6.25,141,1779174000"; d="scan'208";a="87546077" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by orvoesa106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Jul 2026 04:07:48 -0700 X-CSE-ConnectionGUID: qj8BVJ/XRI6zgtwRVeHuag== X-CSE-MsgGUID: hj6+vDsNStmOM/iX4E14dg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,141,1779174000"; d="scan'208";a="248074941" Received: from unknown (HELO [10.239.158.49]) ([10.239.158.49]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Jul 2026 04:07:34 -0700 Message-ID: <25fdb77d-20f6-4b3a-8b3a-dbba0dc47046@intel.com> Date: Wed, 1 Jul 2026 19:07:31 +0800 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 24/46] KVM: guest_memfd: Make in-place conversion the default\ To: Sean Christopherson , Yan Zhao Cc: Ackerley Tng , 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, tabba@google.com, willy@infradead.org, wyihan@google.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 , Vlastimil Babka , 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 References: <20260618-gmem-inplace-conversion-v8-0-9d2959357853@google.com> <20260618-gmem-inplace-conversion-v8-24-9d2959357853@google.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/27/2026 3:06 AM, Sean Christopherson wrote: > On Fri, Jun 26, 2026, Yan Zhao wrote: >> My first impression of gmem_in_place_conversion=true was that it enforces gmem >> in-place conversion. However, it actually only enforces per-gmem private/shared >> attribute. >> My worry was that people might think it's a kernel bug if userspace can still >> have shared memory from other sources after they configured >> gmem_in_place_conversion=true. > Ah, I see where you're coming from. FWIW, truly enforcing in-place conversion > is flat out impossible. E.g. userspace can simply replace the memslot, at which > point the memory effectively reverts to shared. would something like below enforce the in-place conversion? Userspace can create a memslot without gmem fd, but that memslot can only serve as shared memory and cannot be converted. So it doesn't violate the in-place conversion. --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2122,6 +2122,8 @@ static int kvm_set_memory_region(struct kvm *kvm, new->flags = mem->flags; new->userspace_addr = mem->userspace_addr; if (mem->flags & KVM_MEM_GUEST_MEMFD) { + if (gmem_in_place_conversion) + new->flags |= KVM_MEMSLOT_GMEM_ONLY; r = kvm_gmem_bind(kvm, new, mem->guest_memfd, mem->guest_memfd_offset); if (r) goto out;