From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) (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 B171E459AE6; Fri, 11 Sep 2026 09:18:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.17 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789118293; cv=none; b=bcT2vTB3nGzvRcaCl4tD/kwq1l5K3unONkO8pWLxSqheT8GWxZc8OSIO3w8fRZQW7z3ULJev97WAi8ZgslWy77pgZCKhvd8mpazG3InJxbyd2Wc8ubKC88fPPpK2ZkGRm1+ZAxhnZcXtVPyGTJ/722gFALnPD3zTuWTDjaWKye8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789118293; c=relaxed/simple; bh=F4gYdBbmajqkyCINPzu7zVwcdxrJlsDCWKhr3p++93k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=SMXdRe5T2OF6MXuwEcJEkbS6EBrUEhIeFeccDAK97hK/iirEopIe5ln7CDgl24wgmgqcNu0z8P+4jni3TChgSQjY12XP8HtbvedzH/XJBtxz4ONcfKWvT4WFEIQv5GJcoX/BdgDUVj6b6+GLeC7d1vtvvCXt8/xuKQqZ3fH1i/8= 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=cKjeL3h4; arc=none smtp.client-ip=192.198.163.17 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="cKjeL3h4" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1789118292; x=1820654292; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=F4gYdBbmajqkyCINPzu7zVwcdxrJlsDCWKhr3p++93k=; b=cKjeL3h4cMrXQMYZQFCNkOx3Qwhjz1mofLO5X/wGpZffn4/8DHBgsK/D qsHcKYeG/QhjcoeMXSwdEt9bbjH8lDommF9nXkkB/4YJc1Tdxn6qFqmbv QgdZfW+Nq4EZrJsj/Z19bKN3JRo9h7lPxg+eBlcsCwxNzTDdMg41P8WMW /XAk6BpmVHcY7HVpILFlUCFDJx62kfGiJ1MkcjcflfAwfF2npbWyDobC6 g0k3EKViwjiRqDaABuueyR6Ni2a9a2tXS08lWBsYgbz7HiFiv88xDdXNM VBtRdsGuY2oDPBjcDszGxT8zmyACtfZ4llu4BDcpZP875PvbApxJzbrje A==; X-CSE-ConnectionGUID: zavHJylTQcK5ZYtluKCF+g== X-CSE-MsgGUID: qez/0h88TW+fM9Ee8B8vgg== X-IronPort-AV: E=McAfee;i="6800,10657,11901"; a="89450907" X-IronPort-AV: E=Sophos;i="6.27,97,1787036400"; d="scan'208";a="89450907" Received: from fmviesa013.fm.intel.com ([10.60.135.153]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Sep 2026 02:18:11 -0700 X-CSE-ConnectionGUID: LGX/EWeHSPeVzgyLApP5NA== X-CSE-MsgGUID: IuTtAxozTIW46d9/CqObww== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,97,1787036400"; d="scan'208";a="238127" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.124.240.119]) ([10.124.240.119]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Sep 2026 02:17:54 -0700 Message-ID: <9eee9ca8-3818-435f-ae09-78b241050e9e@intel.com> Date: Fri, 11 Sep 2026 17:17:51 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v13 01/44] KVM: guest_memfd: Optimize away conversion overheads via dead-code elimination 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, 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 , John Hubbard , Peter Xu , tarunsahu@google.com, Randy Dunlap , Lorenzo Stoakes , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Fuad Tabba 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: <20260910-gmem-inplace-conversion-v13-0-dd6fbf94f4e1@google.com> <20260910-gmem-inplace-conversion-v13-1-dd6fbf94f4e1@google.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: <20260910-gmem-inplace-conversion-v13-1-dd6fbf94f4e1@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/11/2026 7:55 AM, Ackerley Tng via B4 Relay wrote: > From: Sean Christopherson > > Add and use kvm_arch_has_gmem_convert() to guard guest_memfd's invocation > of arch hooks related to converting memory between private and shared, as > only one half of the x86 CoCo duo needs the runtime hooks (any pre-work is > pure overhead for TDX). At this exact moment, the overhead is negligible, > but that will change when in-place conversion comes along, at which point > to-shared conversions will "need" to find all affected folios prior to > calling into arch code. In quotes because very technically that work could > be pushed to arch code, but that would bleed guest_memfd details into arch > code and would be far worse than adding yet another kvm_arch_has... hook. > > Opportunistically provide the kvm_arch_gmem_make_private() declaration, and > rely on dead-code elimination to eliminate the call to non-existent code > when CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT=n. > > Reported-by: Binbin Wu > Closes: https://lore.kernel.org/all/1ec08cd8-3072-4753-ad5e-cd34956647f8@linux.intel.com > Suggested-by: Ackerley Tng > Signed-off-by: Sean Christopherson > Signed-off-by: Ackerley Tng > Reviewed-by: Fuad Tabba > Reviewed-by: Binbin Wu > Reviewed-by: David Hildenbrand (Arm) Reviewed-by: Xiaoyao Li