From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.11]) (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 CB1BE3B14C6; Wed, 1 Jul 2026 08:05:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.11 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782893142; cv=none; b=uqiyMRH76Ku3aB67QkH5z2Bbsy4O+airmFZvIIe+d9eaNZ4MVsNXzVlzxk6Qn1yd+KFbaLRs3Vgi+JMqEgZmZQpmMhjFInLdFAz90Ib/Mt2p0thW7iWYO0wNdoH4pdnmG/w/KhR+ELLMSZPT2ZXkMXS0GKmOYUr5HEv99ScYkbA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782893142; c=relaxed/simple; bh=DP0eg4B0OM8TO8XnS8C6gHlWxSavTjQl03mk/DOj9RE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=X3ZIxQPx92l8bZuMB158lw1IPu0mq715AjPCOzWV7Yn8XkIZoLgw2ULu2wsXaZXJG6fbtZpeTXoGdOB+BJzZWqqDpUgajsY/SkQaxzrfq8hs0iro4/1fni0e0hbvEzT4Zcd7stP6k23/dKszWQSGJpgF3Q7985uI0qU5z+iusSg= 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=FQnMfZY0; arc=none smtp.client-ip=192.198.163.11 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="FQnMfZY0" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1782893139; x=1814429139; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=DP0eg4B0OM8TO8XnS8C6gHlWxSavTjQl03mk/DOj9RE=; b=FQnMfZY00VYPxz8UpUgTtZallSt5HLZjXvQLkIj4CZE9Xhaj6rSkI5e5 lvSBLjLLeDzMpZcP/8RaPMx1reZKbmKqxCH4QmCOcyM3WNzRKZUzBc1i+ IWNo1OIo0QXVyHQnVEayNSfOIg+cp/5Bxn2NNcqSQnpAwLCaMWmugIdvu HRP0kNWN+3qiU5D+6h2lejaHT8Hf0eiBIP8Vwj6AZ0bavlZR/NOHmcmok q/c5JnE1/PWTJid4Bj8sAVi5A8/gOx+DkmgCX5tg1O96fizfOVNbvReFa KlMckIPpFNf92j7LsSH+1zoR35IorV2anSD1/iscz8HnJqIjyPS1n+rsO A==; X-CSE-ConnectionGUID: l98uhD6OSMS9e2lcfhniWg== X-CSE-MsgGUID: 5TgCtMTJSB2FxG9MwSPVyw== X-IronPort-AV: E=McAfee;i="6800,10657,11833"; a="94217852" X-IronPort-AV: E=Sophos;i="6.24,235,1774335600"; d="scan'208";a="94217852" Received: from fmviesa005.fm.intel.com ([10.60.135.145]) by fmvoesa105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Jul 2026 01:05:26 -0700 X-CSE-ConnectionGUID: lVWuAtoZRb+S8bw6cD6rzw== X-CSE-MsgGUID: G3cj1NKaRzaUjG0LX4qnIg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.24,235,1774335600"; d="scan'208";a="257401196" Received: from unknown (HELO [10.239.158.49]) ([10.239.158.49]) by fmviesa005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Jul 2026 01:05:04 -0700 Message-ID: <3b64e897-93a8-4f9c-88a9-f416ff44b09d@intel.com> Date: Wed, 1 Jul 2026 16:05:00 +0800 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 12/46] KVM: guest_memfd: Only prepare folios for private pages To: 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, tabba@google.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 , Sean Christopherson , 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 Cc: 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-v8-12-9d2959357853@google.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: <20260618-gmem-inplace-conversion-v8-12-9d2959357853@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/19/2026 8:31 AM, Ackerley Tng via B4 Relay wrote: > From: Ackerley Tng > > All-shared guest_memfd used to be only supported for non-CoCo VMs where > preparation doesn't apply. INIT_SHARED is about to be supported for CoCo > VMs in a later patch in this series. > > In addition, KVM_SET_MEMORY_ATTRIBUTES2 is about to be supported in > guest_memfd in a later patch in this series. > > This means that the kvm fault handler may now call kvm_gmem_get_pfn() on a > shared folio for a CoCo VM where preparation applies. I don't get it clear why preparation isn't needed or should not be performed for shared folio. Before this patch, userspace VMM can create the gmem with FLAG_MMAP and FLAG_INIT_SHARED. And KVM always faultin the pfn from gmem. In this case, the gmem is always shared, and kvm_gmem_prepare_folio() is always called when faultin from gmem. So it's OK to call preparation for shared folio, right? Then what is the actual reason we cannot do it now?