From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.20]) (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 ADE8735E94F; Tue, 4 Aug 2026 02:21:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.20 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785810078; cv=none; b=tVkcjfwdUyEzZ0ZnG11tzf66Rq4iWHufRO0VdlDJovkoAt5zn/mtPtf+28VTxyAG6FtiRaQW9KSEUjGzo2QjgI9dzs1Rnhszg3vvyX+ag/Jallk/Rg1dkDoXUseqLuRJA6cO/9ShoBCTYztyVwcPdrl/svlHZPYEGye6Pltv73Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785810078; c=relaxed/simple; bh=+ungbiIvue01mlh3xVvXxn27VLIAH9BlA+zmntBJ5rM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CU9oTbksZieUH8R2wvBL6J+lNDdxqzdeyLfeuFf1tqjFw0SGZ3vNJt3NprB4choa28DsjG59XOYWSma4crWjr6ShwsDYNnVZVuYYVPHq/pq9eUKIxxufrYKjAzSXHb2+dv70VYa7aD0T3ZdNnF1HvjgONwpGDYOERLBhsswU3Zc= 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=csFzeZMQ; arc=none smtp.client-ip=198.175.65.20 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="csFzeZMQ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1785810077; x=1817346077; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=+ungbiIvue01mlh3xVvXxn27VLIAH9BlA+zmntBJ5rM=; b=csFzeZMQQkwiMu7Vlm5Sp/ekudmhx28JVy5zVVCmQr58QiHbJiO3Nzyn KPBzimZhmz6CApZZqBJADE/cR3NTdjQWdmf76ccrEqE4eUPcxqSHlBaOj eEH/hjqCmy8ExDUyhIZZxFQ5U/aJjOAU9Xp6KrNrINVPPrkV6zDD8eER3 m+d+Gj2LHNQbOeH5iPpOkJKIRmdnwt66nV7tFe62SWiVPYYGLS2mi8MoT hPhJqs1KeAz4GaiFEhyyySN2z9uNqX3yprxIPL6Sy8mzBfPw55gJpK/rl /Xc3YRWOkRagEU6z9+3KeVqEYsYQrELmufF6CooxPZiw0z1cL9Nu+SOvN w==; X-CSE-ConnectionGUID: kxSHBAp9T/WPilBLbXpu8Q== X-CSE-MsgGUID: z0pHC6gPTP+cBmwHVBcr6w== X-IronPort-AV: E=McAfee;i="6800,10657,11864"; a="86122340" X-IronPort-AV: E=Sophos;i="6.25,203,1779174000"; d="scan'208";a="86122340" Received: from fmviesa005.fm.intel.com ([10.60.135.145]) by orvoesa112.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Aug 2026 19:21:16 -0700 X-CSE-ConnectionGUID: wexSi1NfRrucV12fpDeh0Q== X-CSE-MsgGUID: Ov1ycEjhQ0S6ouDKkZLVyw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,203,1779174000"; d="scan'208";a="266496543" Received: from fuxiaogu-mobl1.ccr.corp.intel.com (HELO [10.238.208.47]) ([10.238.208.47]) by fmviesa005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Aug 2026 19:21:03 -0700 Message-ID: <8baf2065-b07f-4555-9c16-1330ecec4903@intel.com> Date: Tue, 4 Aug 2026 10:21:00 +0800 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 18/41] KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION To: Sean Christopherson 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, 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 , 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 , 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: <20260728-gmem-inplace-conversion-v9-0-35f9aec2aed2@google.com> <20260728-gmem-inplace-conversion-v9-18-35f9aec2aed2@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 8/1/2026 12:11 AM, Sean Christopherson wrote: > On Fri, Jul 31, 2026, Xiaoyao Li wrote: >> On 7/29/2026 8:35 AM, Ackerley Tng via B4 Relay wrote: >>> From: Ackerley Tng >>> >>> Update tdx_gmem_post_populate() to handle cases where userspace requests >>> "no source page". To handle "no source page", populate (perform >>> TDH.MEM.PAGE.ADD) using memory in-place at the target PFN. >>> >>> Signed-off-by: Sean Christopherson >>> Tested-by: Shivank Garg >>> Signed-off-by: Ackerley Tng >>> --- >>> Documentation/virt/kvm/x86/intel-tdx.rst | 4 ++++ >>> arch/x86/kvm/vmx/tdx.c | 8 +++++--- >>> 2 files changed, 9 insertions(+), 3 deletions(-) >>> >>> diff --git a/Documentation/virt/kvm/x86/intel-tdx.rst b/Documentation/virt/kvm/x86/intel-tdx.rst >>> index 6a222e9d09541..d8d9409120e61 100644 >>> --- a/Documentation/virt/kvm/x86/intel-tdx.rst >>> +++ b/Documentation/virt/kvm/x86/intel-tdx.rst >>> @@ -158,6 +158,10 @@ KVM_TDX_INIT_MEM_REGION >>> Initialize @nr_pages TDX guest private memory starting from @gpa with userspace >>> provided data from @source_addr. @source_addr must be PAGE_SIZE-aligned. >>> +If guest_memfd in-place conversion is enabled, pass 0 for @source_addr >>> +to represent "no source page". A source page is required if in-place >>> +conversion is not enabled or not supported. >>> + >>> Note, before calling this sub command, memory attribute of the range >>> [gpa, gpa + nr_pages] needs to be private. Userspace can use >>> KVM_SET_MEMORY_ATTRIBUTES to set the attribute. >>> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c >>> index d1af0a752e97e..e890da5f18aed 100644 >>> --- a/arch/x86/kvm/vmx/tdx.c >>> +++ b/arch/x86/kvm/vmx/tdx.c >>> @@ -3192,7 +3192,7 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, >>> if (KVM_BUG_ON(kvm_tdx->page_add_src, kvm)) >>> return -EIO; >>> - kvm_tdx->page_add_src = src_page; >>> + kvm_tdx->page_add_src = src_page ?: pfn_to_page(pfn); >>> ret = kvm_tdp_mmu_map_private_pfn(arg->vcpu, gfn, pfn); >>> kvm_tdx->page_add_src = NULL; >>> @@ -3238,7 +3238,8 @@ static int tdx_vcpu_init_mem_region(struct kvm_vcpu *vcpu, struct kvm_tdx_cmd *c >>> if (copy_from_user(®ion, u64_to_user_ptr(cmd->data), sizeof(region))) >>> return -EFAULT; >>> - if (!PAGE_ALIGNED(region.source_addr) || !region.source_addr || >>> + if (!PAGE_ALIGNED(region.source_addr) || >>> + (!gmem_in_place_conversion && !region.source_addr) || >> >> Sorry, I still want to discuss why we only allow in-place PAGE.ADD for >> gmem_in_place_conversion only. Though Yan raised this opinion[1] in previous >> v8, I'm not quite following her argument. So let me try again. >> >> I think in-place PAGE.ADD of TDX doesn't need to depend on >> gmem_in_place_conversion. There are two use cases actually. >> >> 1). Userspace sets the gmem page as private, and invokes the in-place >> PAGE.ADD by passing a 0 source_addr. Due to patch 16, the target PFN will be >> ADD'ed to TD as a all-0 page. >> >> 2). Userspace sets the gmem page as shared, and writes the desired content >> to it. Then converts the page to private, and invokes the in-place PAGE.ADD >> by passing a 0 source_addr. The target PFN will be ADD'ed to TD with desired >> content. >> >> For gmem_in_place_conversion == false, only case 1) is possible. >> For gmem_in_place_conversion == true, both case 1) and 2) are possible. >> >> Basically, this patch is changing the behavior of KVM_TDX_INIT_MEM_REGION. >> Before, it returns -EINVAL when region.source_addr == 0. Now it wants to >> allow the "region.source_addr == 0" case. If we can allow it >> unconditionally, why bother adding the restriction to allow it only when >> gmem_in_place_conversion == true? > > As I said[*] in that thread: > > : Because retroactively adding support for out-of-place conversion is pointless > : (requires a userspace update for a feature that's being deprecated), KVM can't > : generally support using the source for out-of-place conversion (it's effectively > : an obscure zero-page optimization), and IMO rejecting the out-of-place conversion > : scenario is valuable for KVM developers, e.g. to help newcomers understand what > : exactly is and isn't possible. Fair enough. Ackerley, please update the changelog to add the reason why we decided to only support in-place PAGE.ADD for TDX for in-place gmem only. > [*] https://lore.kernel.org/all/akMPZePBdwQlD74H@google.com